Introduce a radix tree data structure for tracking preserved
memory pages in KHO, which will replace the current xarray-based
implementation.
The primary motivation for this change is to eliminate the need for
serialization. By marking preserved pages directly in the new KHO
radix tree and passing them to the next kernel, the entire
serialization process can be removed. This ultimately allows for the
removal of the KHO finalize and abort states, simplifying the overall
design.
The preserved page physical address and its order are encoded in to a
value. The KHO radix tree has multiple level of nodes where each node
is a table contining a descriptor to the next level of nodes. The
encoded value get split and stored its parts along the tree
traversal. The tree traversal ends with the `kho_bitmap_table`, where
each bit represents a single preserved page.
Instead of serializing the memory map, the first kernel store the KHO
radix tree root in the FDT. This KHO radix tree root is passed to the
second kernel after kexec, hence elimitated the KHO finalize and abort
states.
The second kernel walks the passed-in KHO radix tree from its root. It
restores the memory pages and their orders by decoding the value
stored in the KHO radix tree.
This architectural shift to using a shared radix tree structure
simplifies the KHO design and eliminates the overhead of serializing
and deserializing the preserved memory map.
Signed-off-by: Jason Miu <jasonmiu@google.com>
---
include/linux/kexec_handover.h | 17 -
kernel/kexec_handover.c | 729 +++++++++++++++------------------
2 files changed, 322 insertions(+), 424 deletions(-)
diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 348844cffb13..c8229cb11f4b 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -19,23 +19,6 @@ enum kho_event {
struct folio;
struct notifier_block;
-#define DECLARE_KHOSER_PTR(name, type) \
- union { \
- phys_addr_t phys; \
- type ptr; \
- } name
-#define KHOSER_STORE_PTR(dest, val) \
- ({ \
- typeof(val) v = val; \
- typecheck(typeof((dest).ptr), v); \
- (dest).phys = virt_to_phys(v); \
- })
-#define KHOSER_LOAD_PTR(src) \
- ({ \
- typeof(src) s = src; \
- (typeof((s).ptr))((s).phys ? phys_to_virt((s).phys) : NULL); \
- })
-
struct kho_serialization;
#ifdef CONFIG_KEXEC_HANDOVER
diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index ecd1ac210dbd..34cf0ce4f359 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -18,6 +18,7 @@
#include <linux/memblock.h>
#include <linux/notifier.h>
#include <linux/page-isolation.h>
+#include <linux/rwsem.h>
#include <asm/early_ioremap.h>
@@ -29,7 +30,7 @@
#include "kexec_internal.h"
#define KHO_FDT_COMPATIBLE "kho-v1"
-#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
+#define PROP_PRESERVED_PAGE_RADIX_TREE "preserved-page-radix-tree"
#define PROP_SUB_FDT "fdt"
static bool kho_enable __ro_after_init;
@@ -46,143 +47,306 @@ static int __init kho_parse_enable(char *p)
}
early_param("kho", kho_parse_enable);
+typedef int (*kho_radix_tree_walk_callback_t)(unsigned long encoded);
+
/*
- * Keep track of memory that is to be preserved across KHO.
+ * The KHO radix tree tracks preserved memory pages. It is a hierarchical
+ * structure that starts with a single root `kho_radix_tree`. This single
+ * tree stores pages of all orders.
+ *
+ * This is achieved by encoding the page's physical address and its order into
+ * a single `unsigned long` value. This encoded value is then used to traverse
+ * the tree.
+ *
+ * The tree hierarchy is shown below:
+ *
+ * kho_radix_tree_root
+ * +-------------------+
+ * | Level 6 | (struct kho_radix_tree)
+ * +-------------------+
+ * |
+ * v
+ * +-------------------+
+ * | Level 5 | (struct kho_radix_tree)
+ * +-------------------+
+ * |
+ * | ... (intermediate levels)
+ * |
+ * v
+ * +-------------------+
+ * | Level 1 | (struct kho_bitmap_table)
+ * +-------------------+
+ *
+ * The following diagram illustrates how the encoded value is split into
+ * indices for the tree levels:
*
- * The serializing side uses two levels of xarrays to manage chunks of per-order
- * 512 byte bitmaps. For instance if PAGE_SIZE = 4096, the entire 1G order of a
- * 1TB system would fit inside a single 512 byte bitmap. For order 0 allocations
- * each bitmap will cover 16M of address space. Thus, for 16G of memory at most
- * 512K of bitmap memory will be needed for order 0.
+ * 63:60 59:51 50:42 41:33 32:24 23:15 14:0
+ * +---------+--------+--------+--------+--------+--------+-----------------+
+ * | 0 | Lv 6 | Lv 5 | Lv 4 | Lv 3 | Lv 2 | Lv 1 (bitmap) |
+ * +---------+--------+--------+--------+--------+--------+-----------------+
*
- * This approach is fully incremental, as the serialization progresses folios
- * can continue be aggregated to the tracker. The final step, immediately prior
- * to kexec would serialize the xarray information into a linked list for the
- * successor kernel to parse.
+ * Each `kho_radix_tree` (Levels 2-6) and `kho_bitmap_table` (Level 1) is
+ * PAGE_SIZE. Each entry in a `kho_radix_tree` is a descriptor (a physical
+ * address) pointing to the next level node. For Level 2 `kho_radix_tree`
+ * nodes, these descriptors point to a `kho_bitmap_table`. The final
+ * `kho_bitmap_table` is a bitmap where each set bit represents a single
+ * preserved page.
*/
+struct kho_radix_tree {
+ unsigned long table[PAGE_SIZE / sizeof(unsigned long)];
+};
-#define PRESERVE_BITS (512 * 8)
-
-struct kho_mem_phys_bits {
- DECLARE_BITMAP(preserve, PRESERVE_BITS);
+struct kho_bitmap_table {
+ unsigned long bitmaps[PAGE_SIZE / sizeof(unsigned long)];
};
-struct kho_mem_phys {
+/*
+ * `kho_radix_tree_root` points to a page thats serves as the root of the
+ * KHO radix tree. This page is allocated during KHO module initialization.
+ * Its physical address is written to the FDT and passed to the next kernel
+ * during kexec.
+ */
+static struct kho_radix_tree *kho_radix_tree_root;
+static DECLARE_RWSEM(kho_radix_tree_root_sem);
+
+static int kho_radix_tree_max_depth(void)
+{
+ int page_offset_bit_num = BITS_PER_LONG - PAGE_SHIFT;
+ int order_bit_num = ilog2(__roundup_pow_of_two(page_offset_bit_num));
+ int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
+ int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
+ int table_level_num = DIV_ROUND_UP(page_offset_bit_num -
+ bitmap_bit_num + order_bit_num,
+ table_bit_num);
+
/*
- * Points to kho_mem_phys_bits, a sparse bitmap array. Each bit is sized
- * to order.
+ * The total tree depth is the number of intermediate levels
+ * and 1 bitmap level.
*/
- struct xarray phys_bits;
-};
+ return table_level_num + 1;
+}
-struct kho_mem_track {
- /* Points to kho_mem_phys, each order gets its own bitmap tree */
- struct xarray orders;
-};
+static struct kho_radix_tree *kho_alloc_radix_tree(void)
+{
+ return (struct kho_radix_tree *)get_zeroed_page(GFP_KERNEL);
+}
-struct khoser_mem_chunk;
+/*
+ * The KHO radix tree tracks preserved pages by encoding a page's physical
+ * address (pa) and its order into a single unsigned long value. This value
+ * is then used to traverse the tree. The encoded value is composed of two
+ * parts: the 'order bits' in the upper part and the 'page offset' in the
+ * lower part.
+ *
+ * <-- Higher Bits ------------------------------------ Lower Bits -->
+ * +--------------------------+-----------------------------------------+
+ * | Order Bits | Page Offset |
+ * +--------------------------+-----------------------------------------+
+ * | ... 0 0 1 0 0 ... | pa >> (PAGE_SHIFT + order) |
+ * +--------------------------+-----------------------------------------+
+ * ^
+ * |
+ * This single '1' bit's position
+ * uniquely identifies the 'order'.
+ *
+ *
+ * Page Offset:
+ * The 'page offset' is the physical address normalized for its order. It
+ * effectively represents the page offset for the given order.
+ *
+ * Order Bits:
+ * The 'order bits' encode the page order by setting a single bit at a
+ * specific position. The position of this bit itself represents the order.
+ *
+ * For instance, on a 64-bit system with 4KB pages (PAGE_SHIFT = 12), the
+ * maximum range for a page offset (for order 0) is 52 bits (64 - 12). This
+ * offset occupies bits [0-51]. For order 0, the order bit is set at
+ * position 52.
+ *
+ * As the order increases, the number of bits required for the 'page offset'
+ * decreases. For example, order 1 requires one less bit for its page
+ * offset. This allows its order bit to be set at position 51 without
+ * conflicting with the page offset bits.
+ *
+ * This scheme ensures that the single order bit is always in a higher
+ * position than any bit used by the page offset for that same order,
+ * preventing collisions.
+ */
+static unsigned long kho_radix_encode(unsigned long pa, unsigned int order)
+{
+ unsigned long h = 1UL << (BITS_PER_LONG - PAGE_SHIFT - order);
+ unsigned long l = pa >> (PAGE_SHIFT + order);
-struct kho_serialization {
- struct page *fdt;
- struct list_head fdt_list;
- struct dentry *sub_fdt_dir;
- struct kho_mem_track track;
- /* First chunk of serialized preserved memory map */
- struct khoser_mem_chunk *preserved_mem_map;
-};
+ return h | l;
+}
-static void *xa_load_or_alloc(struct xarray *xa, unsigned long index, size_t sz)
+static unsigned long kho_radix_decode(unsigned long encoded, unsigned int *order)
{
- void *elm, *res;
+ unsigned long order_bit = fls64(encoded);
+ unsigned long pa;
- elm = xa_load(xa, index);
- if (elm)
- return elm;
+ *order = BITS_PER_LONG - PAGE_SHIFT - order_bit + 1;
+ pa = encoded << (PAGE_SHIFT + *order);
- elm = kzalloc(sz, GFP_KERNEL);
- if (!elm)
- return ERR_PTR(-ENOMEM);
-
- res = xa_cmpxchg(xa, index, NULL, elm, GFP_KERNEL);
- if (xa_is_err(res))
- res = ERR_PTR(xa_err(res));
+ return pa;
+}
- if (res) {
- kfree(elm);
- return res;
+static unsigned long kho_radix_get_index(unsigned long encoded, int level)
+{
+ int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
+ int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
+ unsigned long mask;
+ int s;
+
+ if (level == 1) {
+ s = 0;
+ mask = (1UL << bitmap_bit_num) - 1;
+ } else {
+ s = ((level - 2) * table_bit_num) + bitmap_bit_num;
+ mask = (1UL << table_bit_num) - 1;
}
- return elm;
+ return (encoded >> s) & mask;
}
-static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
- unsigned long end_pfn)
+static int kho_radix_set_bitmap(struct kho_bitmap_table *bit_tlb, unsigned long offset)
{
- struct kho_mem_phys_bits *bits;
- struct kho_mem_phys *physxa;
+ if (!bit_tlb ||
+ offset >= PAGE_SIZE * BITS_PER_BYTE)
+ return -EINVAL;
- while (pfn < end_pfn) {
- const unsigned int order =
- min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
- const unsigned long pfn_high = pfn >> order;
+ set_bit(offset, bit_tlb->bitmaps);
+ return 0;
+}
- physxa = xa_load(&track->orders, order);
- if (!physxa)
- continue;
+static int kho_radix_preserve_page(unsigned long pa, unsigned int order)
+{
+ unsigned long encoded = kho_radix_encode(pa, order);
+ int num_tree_level = kho_radix_tree_max_depth();
+ struct kho_radix_tree *current_tree, *new_tree;
+ struct kho_bitmap_table *bitmap_table;
+ int err = 0;
+ int i, idx;
- bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
- if (!bits)
- continue;
+ down_write(&kho_radix_tree_root_sem);
- clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+ current_tree = kho_radix_tree_root;
- pfn += 1 << order;
+ /* Go from high levels to low levels */
+ for (i = num_tree_level; i >= 1; i--) {
+ idx = kho_radix_get_index(encoded, i);
+
+ if (i == 1) {
+ bitmap_table = (struct kho_bitmap_table *)current_tree;
+ err = kho_radix_set_bitmap(bitmap_table, idx);
+ goto out;
+ }
+
+ if (!current_tree->table[idx]) {
+ new_tree = kho_alloc_radix_tree();
+ if (!new_tree) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ current_tree->table[idx] =
+ (unsigned long)virt_to_phys(new_tree);
+ }
+
+ current_tree = (struct kho_radix_tree *)
+ phys_to_virt(current_tree->table[idx]);
}
+
+out:
+ up_write(&kho_radix_tree_root_sem);
+ return err;
}
-static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
- unsigned int order)
+static int kho_radix_walk_bitmaps(struct kho_bitmap_table *bit_tlb,
+ unsigned long offset,
+ kho_radix_tree_walk_callback_t cb)
{
- struct kho_mem_phys_bits *bits;
- struct kho_mem_phys *physxa, *new_physxa;
- const unsigned long pfn_high = pfn >> order;
+ unsigned long encoded = offset << (PAGE_SHIFT + ilog2(BITS_PER_BYTE));
+ unsigned long *bitmap = (unsigned long *)bit_tlb;
+ int err = 0;
+ int i;
- might_sleep();
+ for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
+ err = cb(encoded | i);
+ if (err)
+ return err;
+ }
- physxa = xa_load(&track->orders, order);
- if (!physxa) {
- int err;
+ return 0;
+}
- new_physxa = kzalloc(sizeof(*physxa), GFP_KERNEL);
- if (!new_physxa)
- return -ENOMEM;
+static int kho_radix_walk_trees(struct kho_radix_tree *root, int level,
+ unsigned long offset,
+ kho_radix_tree_walk_callback_t cb)
+{
+ int level_shift = ilog2(PAGE_SIZE / sizeof(unsigned long));
+ struct kho_radix_tree *next_tree;
+ unsigned long encoded, i;
+ int err = 0;
- xa_init(&new_physxa->phys_bits);
- physxa = xa_cmpxchg(&track->orders, order, NULL, new_physxa,
- GFP_KERNEL);
+ if (level == 1) {
+ encoded = offset;
+ return kho_radix_walk_bitmaps((struct kho_bitmap_table *)root,
+ encoded, cb);
+ }
- err = xa_err(physxa);
- if (err || physxa) {
- xa_destroy(&new_physxa->phys_bits);
- kfree(new_physxa);
+ for (i = 0; i < PAGE_SIZE / sizeof(unsigned long); i++) {
+ if (root->table[i]) {
+ encoded = offset << level_shift | i;
+ next_tree = (struct kho_radix_tree *)
+ phys_to_virt(root->table[i]);
+ err = kho_radix_walk_trees(next_tree, level - 1, encoded, cb);
if (err)
return err;
- } else {
- physxa = new_physxa;
}
}
- bits = xa_load_or_alloc(&physxa->phys_bits, pfn_high / PRESERVE_BITS,
- sizeof(*bits));
- if (IS_ERR(bits))
- return PTR_ERR(bits);
+ return 0;
+}
- set_bit(pfn_high % PRESERVE_BITS, bits->preserve);
+static int kho_memblock_reserve(phys_addr_t pa, int order)
+{
+ int sz = 1 << (order + PAGE_SHIFT);
+ struct page *page = phys_to_page(pa);
+
+ memblock_reserve(pa, sz);
+ memblock_reserved_mark_noinit(pa, sz);
+ page->private = order;
return 0;
}
+static int kho_radix_walk_trees_callback(unsigned long encoded)
+{
+ unsigned int order;
+ unsigned long pa;
+
+ pa = kho_radix_decode(encoded, &order);
+
+ return kho_memblock_reserve(pa, order);
+}
+
+struct kho_serialization {
+ struct page *fdt;
+ struct list_head fdt_list;
+ struct dentry *sub_fdt_dir;
+};
+
+static int __kho_preserve_order(unsigned long pfn, unsigned int order)
+{
+ unsigned long pa = PFN_PHYS(pfn);
+
+ might_sleep();
+
+ return kho_radix_preserve_page(pa, order);
+}
+
/* almost as free_reserved_page(), just don't free the page */
static void kho_restore_page(struct page *page, unsigned int order)
{
@@ -224,152 +388,29 @@ struct folio *kho_restore_folio(phys_addr_t phys)
}
EXPORT_SYMBOL_GPL(kho_restore_folio);
-/* Serialize and deserialize struct kho_mem_phys across kexec
- *
- * Record all the bitmaps in a linked list of pages for the next kernel to
- * process. Each chunk holds bitmaps of the same order and each block of bitmaps
- * starts at a given physical address. This allows the bitmaps to be sparse. The
- * xarray is used to store them in a tree while building up the data structure,
- * but the KHO successor kernel only needs to process them once in order.
- *
- * All of this memory is normal kmalloc() memory and is not marked for
- * preservation. The successor kernel will remain isolated to the scratch space
- * until it completes processing this list. Once processed all the memory
- * storing these ranges will be marked as free.
- */
-
-struct khoser_mem_bitmap_ptr {
- phys_addr_t phys_start;
- DECLARE_KHOSER_PTR(bitmap, struct kho_mem_phys_bits *);
-};
-
-struct khoser_mem_chunk_hdr {
- DECLARE_KHOSER_PTR(next, struct khoser_mem_chunk *);
- unsigned int order;
- unsigned int num_elms;
-};
-
-#define KHOSER_BITMAP_SIZE \
- ((PAGE_SIZE - sizeof(struct khoser_mem_chunk_hdr)) / \
- sizeof(struct khoser_mem_bitmap_ptr))
-
-struct khoser_mem_chunk {
- struct khoser_mem_chunk_hdr hdr;
- struct khoser_mem_bitmap_ptr bitmaps[KHOSER_BITMAP_SIZE];
-};
-
-static_assert(sizeof(struct khoser_mem_chunk) == PAGE_SIZE);
-
-static struct khoser_mem_chunk *new_chunk(struct khoser_mem_chunk *cur_chunk,
- unsigned long order)
-{
- struct khoser_mem_chunk *chunk;
-
- chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
- if (!chunk)
- return NULL;
- chunk->hdr.order = order;
- if (cur_chunk)
- KHOSER_STORE_PTR(cur_chunk->hdr.next, chunk);
- return chunk;
-}
-
-static void kho_mem_ser_free(struct khoser_mem_chunk *first_chunk)
-{
- struct khoser_mem_chunk *chunk = first_chunk;
-
- while (chunk) {
- struct khoser_mem_chunk *tmp = chunk;
-
- chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
- kfree(tmp);
- }
-}
-
-static int kho_mem_serialize(struct kho_serialization *ser)
-{
- struct khoser_mem_chunk *first_chunk = NULL;
- struct khoser_mem_chunk *chunk = NULL;
- struct kho_mem_phys *physxa;
- unsigned long order;
-
- xa_for_each(&ser->track.orders, order, physxa) {
- struct kho_mem_phys_bits *bits;
- unsigned long phys;
-
- chunk = new_chunk(chunk, order);
- if (!chunk)
- goto err_free;
-
- if (!first_chunk)
- first_chunk = chunk;
-
- xa_for_each(&physxa->phys_bits, phys, bits) {
- struct khoser_mem_bitmap_ptr *elm;
-
- if (chunk->hdr.num_elms == ARRAY_SIZE(chunk->bitmaps)) {
- chunk = new_chunk(chunk, order);
- if (!chunk)
- goto err_free;
- }
-
- elm = &chunk->bitmaps[chunk->hdr.num_elms];
- chunk->hdr.num_elms++;
- elm->phys_start = (phys * PRESERVE_BITS)
- << (order + PAGE_SHIFT);
- KHOSER_STORE_PTR(elm->bitmap, bits);
- }
- }
-
- ser->preserved_mem_map = first_chunk;
-
- return 0;
-
-err_free:
- kho_mem_ser_free(first_chunk);
- return -ENOMEM;
-}
-
-static void __init deserialize_bitmap(unsigned int order,
- struct khoser_mem_bitmap_ptr *elm)
-{
- struct kho_mem_phys_bits *bitmap = KHOSER_LOAD_PTR(elm->bitmap);
- unsigned long bit;
-
- for_each_set_bit(bit, bitmap->preserve, PRESERVE_BITS) {
- int sz = 1 << (order + PAGE_SHIFT);
- phys_addr_t phys =
- elm->phys_start + (bit << (order + PAGE_SHIFT));
- struct page *page = phys_to_page(phys);
-
- memblock_reserve(phys, sz);
- memblock_reserved_mark_noinit(phys, sz);
- page->private = order;
- }
-}
-
static void __init kho_mem_deserialize(const void *fdt)
{
- struct khoser_mem_chunk *chunk;
const phys_addr_t *mem;
int len;
+ struct kho_radix_tree *tree_root;
- mem = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
+ /* Retrieve the KHO radix tree from passed-in FDT. */
+ mem = fdt_getprop(fdt, 0, PROP_PRESERVED_PAGE_RADIX_TREE, &len);
if (!mem || len != sizeof(*mem)) {
- pr_err("failed to get preserved memory bitmaps\n");
+ pr_err("failed to get preserved KHO memory tree\n");
return;
}
- chunk = *mem ? phys_to_virt(*mem) : NULL;
- while (chunk) {
- unsigned int i;
+ tree_root = *mem ?
+ (struct kho_radix_tree *)phys_to_virt(*mem) :
+ NULL;
- for (i = 0; i != chunk->hdr.num_elms; i++)
- deserialize_bitmap(chunk->hdr.order,
- &chunk->bitmaps[i]);
- chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
- }
+ if (!tree_root)
+ return;
+
+ kho_radix_walk_trees(tree_root, kho_radix_tree_max_depth(),
+ 0, kho_radix_walk_trees_callback);
}
/*
@@ -633,25 +674,15 @@ EXPORT_SYMBOL_GPL(kho_add_subtree);
struct kho_out {
struct blocking_notifier_head chain_head;
-
struct dentry *dir;
-
- struct mutex lock; /* protects KHO FDT finalization */
-
struct kho_serialization ser;
- bool finalized;
};
static struct kho_out kho_out = {
.chain_head = BLOCKING_NOTIFIER_INIT(kho_out.chain_head),
- .lock = __MUTEX_INITIALIZER(kho_out.lock),
.ser = {
.fdt_list = LIST_HEAD_INIT(kho_out.ser.fdt_list),
- .track = {
- .orders = XARRAY_INIT(kho_out.ser.track.orders, 0),
- },
},
- .finalized = false,
};
int register_kho_notifier(struct notifier_block *nb)
@@ -679,12 +710,8 @@ int kho_preserve_folio(struct folio *folio)
{
const unsigned long pfn = folio_pfn(folio);
const unsigned int order = folio_order(folio);
- struct kho_mem_track *track = &kho_out.ser.track;
- if (kho_out.finalized)
- return -EBUSY;
-
- return __kho_preserve_order(track, pfn, order);
+ return __kho_preserve_order(pfn, order);
}
EXPORT_SYMBOL_GPL(kho_preserve_folio);
@@ -701,14 +728,8 @@ EXPORT_SYMBOL_GPL(kho_preserve_folio);
int kho_preserve_phys(phys_addr_t phys, size_t size)
{
unsigned long pfn = PHYS_PFN(phys);
- unsigned long failed_pfn = 0;
- const unsigned long start_pfn = pfn;
const unsigned long end_pfn = PHYS_PFN(phys + size);
int err = 0;
- struct kho_mem_track *track = &kho_out.ser.track;
-
- if (kho_out.finalized)
- return -EBUSY;
if (!PAGE_ALIGNED(phys) || !PAGE_ALIGNED(size))
return -EINVAL;
@@ -717,19 +738,14 @@ int kho_preserve_phys(phys_addr_t phys, size_t size)
const unsigned int order =
min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
- err = __kho_preserve_order(track, pfn, order);
- if (err) {
- failed_pfn = pfn;
- break;
- }
+ err = __kho_preserve_order(pfn, order);
+ if (err)
+ return err;
pfn += 1 << order;
}
- if (err)
- __kho_unpreserve(track, start_pfn, failed_pfn);
-
- return err;
+ return 0;
}
EXPORT_SYMBOL_GPL(kho_preserve_phys);
@@ -737,150 +753,6 @@ EXPORT_SYMBOL_GPL(kho_preserve_phys);
static struct dentry *debugfs_root;
-static int kho_out_update_debugfs_fdt(void)
-{
- int err = 0;
- struct fdt_debugfs *ff, *tmp;
-
- if (kho_out.finalized) {
- err = kho_debugfs_fdt_add(&kho_out.ser.fdt_list, kho_out.dir,
- "fdt", page_to_virt(kho_out.ser.fdt));
- } else {
- list_for_each_entry_safe(ff, tmp, &kho_out.ser.fdt_list, list) {
- debugfs_remove(ff->file);
- list_del(&ff->list);
- kfree(ff);
- }
- }
-
- return err;
-}
-
-static int kho_abort(void)
-{
- int err;
- unsigned long order;
- struct kho_mem_phys *physxa;
-
- xa_for_each(&kho_out.ser.track.orders, order, physxa) {
- struct kho_mem_phys_bits *bits;
- unsigned long phys;
-
- xa_for_each(&physxa->phys_bits, phys, bits)
- kfree(bits);
-
- xa_destroy(&physxa->phys_bits);
- kfree(physxa);
- }
- xa_destroy(&kho_out.ser.track.orders);
-
- if (kho_out.ser.preserved_mem_map) {
- kho_mem_ser_free(kho_out.ser.preserved_mem_map);
- kho_out.ser.preserved_mem_map = NULL;
- }
-
- err = blocking_notifier_call_chain(&kho_out.chain_head, KEXEC_KHO_ABORT,
- NULL);
- err = notifier_to_errno(err);
-
- if (err)
- pr_err("Failed to abort KHO finalization: %d\n", err);
-
- return err;
-}
-
-static int kho_finalize(void)
-{
- int err = 0;
- u64 *preserved_mem_map;
- void *fdt = page_to_virt(kho_out.ser.fdt);
-
- err |= fdt_create(fdt, PAGE_SIZE);
- err |= fdt_finish_reservemap(fdt);
- err |= fdt_begin_node(fdt, "");
- err |= fdt_property_string(fdt, "compatible", KHO_FDT_COMPATIBLE);
- /**
- * Reserve the preserved-memory-map property in the root FDT, so
- * that all property definitions will precede subnodes created by
- * KHO callers.
- */
- err |= fdt_property_placeholder(fdt, PROP_PRESERVED_MEMORY_MAP,
- sizeof(*preserved_mem_map),
- (void **)&preserved_mem_map);
- if (err)
- goto abort;
-
- err = kho_preserve_folio(page_folio(kho_out.ser.fdt));
- if (err)
- goto abort;
-
- err = blocking_notifier_call_chain(&kho_out.chain_head,
- KEXEC_KHO_FINALIZE, &kho_out.ser);
- err = notifier_to_errno(err);
- if (err)
- goto abort;
-
- err = kho_mem_serialize(&kho_out.ser);
- if (err)
- goto abort;
-
- *preserved_mem_map = (u64)virt_to_phys(kho_out.ser.preserved_mem_map);
-
- err |= fdt_end_node(fdt);
- err |= fdt_finish(fdt);
-
-abort:
- if (err) {
- pr_err("Failed to convert KHO state tree: %d\n", err);
- kho_abort();
- }
-
- return err;
-}
-
-static int kho_out_finalize_get(void *data, u64 *val)
-{
- mutex_lock(&kho_out.lock);
- *val = kho_out.finalized;
- mutex_unlock(&kho_out.lock);
-
- return 0;
-}
-
-static int kho_out_finalize_set(void *data, u64 _val)
-{
- int ret = 0;
- bool val = !!_val;
-
- mutex_lock(&kho_out.lock);
-
- if (val == kho_out.finalized) {
- if (kho_out.finalized)
- ret = -EEXIST;
- else
- ret = -ENOENT;
- goto unlock;
- }
-
- if (val)
- ret = kho_finalize();
- else
- ret = kho_abort();
-
- if (ret)
- goto unlock;
-
- kho_out.finalized = val;
- ret = kho_out_update_debugfs_fdt();
-
-unlock:
- mutex_unlock(&kho_out.lock);
- return ret;
-}
-
-DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get,
- kho_out_finalize_set, "%llu\n");
-
static int scratch_phys_show(struct seq_file *m, void *v)
{
for (int i = 0; i < kho_scratch_cnt; i++)
@@ -921,11 +793,6 @@ static __init int kho_out_debugfs_init(void)
if (IS_ERR(f))
goto err_rmdir;
- f = debugfs_create_file("finalize", 0600, dir, NULL,
- &fops_kho_out_finalize);
- if (IS_ERR(f))
- goto err_rmdir;
-
kho_out.dir = dir;
kho_out.ser.sub_fdt_dir = sub_fdt_dir;
return 0;
@@ -1037,6 +904,37 @@ static __init int kho_in_debugfs_init(const void *fdt)
return err;
}
+static int kho_out_fdt_init(void)
+{
+ int err = 0;
+ void *fdt = page_to_virt(kho_out.ser.fdt);
+ u64 *preserved_radix_tree_root;
+
+ err |= fdt_create(fdt, PAGE_SIZE);
+ err |= fdt_finish_reservemap(fdt);
+ err |= fdt_begin_node(fdt, "");
+ err |= fdt_property_string(fdt, "compatible", KHO_FDT_COMPATIBLE);
+
+ err |= fdt_property_placeholder(fdt, PROP_PRESERVED_PAGE_RADIX_TREE,
+ sizeof(*preserved_radix_tree_root),
+ (void **)&preserved_radix_tree_root);
+ if (err)
+ goto abort;
+
+ down_read(&kho_radix_tree_root_sem);
+ *preserved_radix_tree_root = (u64)virt_to_phys(kho_radix_tree_root);
+ up_read(&kho_radix_tree_root_sem);
+
+ err |= fdt_end_node(fdt);
+ err |= fdt_finish(fdt);
+
+abort:
+ if (err)
+ pr_err("Failed to convert KHO memory tree: %d\n", err);
+
+ return err;
+}
+
static __init int kho_init(void)
{
int err = 0;
@@ -1051,15 +949,29 @@ static __init int kho_init(void)
goto err_free_scratch;
}
+ kho_radix_tree_root = (struct kho_radix_tree *)
+ kzalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!kho_radix_tree_root) {
+ err = -ENOMEM;
+ goto err_free_fdt;
+ }
+
+ err = kho_out_fdt_init();
+ if (err)
+ goto err_free_kho_radix_tree_root;
+
debugfs_root = debugfs_create_dir("kho", NULL);
if (IS_ERR(debugfs_root)) {
err = -ENOENT;
- goto err_free_fdt;
+ goto err_free_kho_radix_tree_root;
}
err = kho_out_debugfs_init();
if (err)
- goto err_free_fdt;
+ goto err_free_kho_radix_tree_root;
+
+ /* Preserve the memory page of FDT for the next kernel */
+ kho_preserve_phys(page_to_phys(kho_out.ser.fdt), PAGE_SIZE);
if (fdt) {
err = kho_in_debugfs_init(fdt);
@@ -1087,6 +999,9 @@ static __init int kho_init(void)
return 0;
+err_free_kho_radix_tree_root:
+ kfree(kho_radix_tree_root);
+ kho_radix_tree_root = NULL;
err_free_fdt:
put_page(kho_out.ser.fdt);
kho_out.ser.fdt = NULL;
--
2.51.0.618.g983fd99d29-googOn Tue, Sep 30, 2025 at 06:19:39PM -0700, Jason Miu wrote:
> @@ -29,7 +30,7 @@
> #include "kexec_internal.h"
>
> #define KHO_FDT_COMPATIBLE "kho-v1"
We don't bump this?
> -#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
> +#define PROP_PRESERVED_PAGE_RADIX_TREE "preserved-page-radix-tree"
> #define PROP_SUB_FDT "fdt"
I'de really like to see all of these sorts of definitions in some
structured ABI header not open coded all over the place..
> /*
> + * The KHO radix tree tracks preserved memory pages. It is a hierarchical
> + * structure that starts with a single root `kho_radix_tree`. This single
> + * tree stores pages of all orders.
> + *
> + * This is achieved by encoding the page's physical address and its order into
> + * a single `unsigned long` value. This encoded value is then used to traverse
> + * the tree.
> + *
> + * The tree hierarchy is shown below:
> + *
> + * kho_radix_tree_root
> + * +-------------------+
> + * | Level 6 | (struct kho_radix_tree)
> + * +-------------------+
> + * |
> + * v
> + * +-------------------+
> + * | Level 5 | (struct kho_radix_tree)
> + * +-------------------+
> + * |
> + * | ... (intermediate levels)
> + * |
> + * v
> + * +-------------------+
> + * | Level 1 | (struct kho_bitmap_table)
> + * +-------------------+
> + *
> + * The following diagram illustrates how the encoded value is split into
> + * indices for the tree levels:
> *
> + * 63:60 59:51 50:42 41:33 32:24 23:15 14:0
> + * +---------+--------+--------+--------+--------+--------+-----------------+
> + * | 0 | Lv 6 | Lv 5 | Lv 4 | Lv 3 | Lv 2 | Lv 1 (bitmap) |
> + * +---------+--------+--------+--------+--------+--------+-----------------+
> *
> + * Each `kho_radix_tree` (Levels 2-6) and `kho_bitmap_table` (Level 1) is
> + * PAGE_SIZE. Each entry in a `kho_radix_tree` is a descriptor (a physical
> + * address) pointing to the next level node. For Level 2 `kho_radix_tree`
> + * nodes, these descriptors point to a `kho_bitmap_table`. The final
> + * `kho_bitmap_table` is a bitmap where each set bit represents a single
> + * preserved page.
Maybe a note that this is example is for PAGE_SIZE=4k.
> */
> +struct kho_radix_tree {
> + unsigned long table[PAGE_SIZE / sizeof(unsigned long)];
This should be phys_addr_t.
> +};
You dropped the macros so now we don't know these are actually
pointers to 'struct kho_radix_tree'
> +/*
> + * `kho_radix_tree_root` points to a page thats serves as the root of the
> + * KHO radix tree. This page is allocated during KHO module initialization.
> + * Its physical address is written to the FDT and passed to the next kernel
> + * during kexec.
> + */
> +static struct kho_radix_tree *kho_radix_tree_root;
> +static DECLARE_RWSEM(kho_radix_tree_root_sem);
> +
> +static int kho_radix_tree_max_depth(void)
> +{
> + int page_offset_bit_num = BITS_PER_LONG - PAGE_SHIFT;
> + int order_bit_num = ilog2(__roundup_pow_of_two(page_offset_bit_num));
> + int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
> + int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
> + int table_level_num = DIV_ROUND_UP(page_offset_bit_num -
> + bitmap_bit_num + order_bit_num,
> + table_bit_num);
All should be unsigned int. Below I suggest to put it in an enum and
use different names.. And since the function is constant it can just
be an enum TOP_LEVEL too.
> +/*
> + * The KHO radix tree tracks preserved pages by encoding a page's physical
> + * address (pa) and its order into a single unsigned long value. This value
> + * is then used to traverse the tree. The encoded value is composed of two
> + * parts: the 'order bits' in the upper part and the 'page offset' in the
> + * lower part.
> + *
> + * <-- Higher Bits ------------------------------------ Lower Bits -->
> + * +--------------------------+-----------------------------------------+
> + * | Order Bits | Page Offset |
> + * +--------------------------+-----------------------------------------+
> + * | ... 0 0 1 0 0 ... | pa >> (PAGE_SHIFT + order) |
> + * +--------------------------+-----------------------------------------+
> + * ^
> + * |
> + * This single '1' bit's position
> + * uniquely identifies the 'order'.
> + *
> + *
> + * Page Offset:
> + * The 'page offset' is the physical address normalized for its order. It
> + * effectively represents the page offset for the given order.
> + *
> + * Order Bits:
> + * The 'order bits' encode the page order by setting a single bit at a
> + * specific position. The position of this bit itself represents the order.
> + *
> + * For instance, on a 64-bit system with 4KB pages (PAGE_SHIFT = 12), the
> + * maximum range for a page offset (for order 0) is 52 bits (64 - 12). This
> + * offset occupies bits [0-51]. For order 0, the order bit is set at
> + * position 52.
> + *
> + * As the order increases, the number of bits required for the 'page offset'
> + * decreases. For example, order 1 requires one less bit for its page
> + * offset. This allows its order bit to be set at position 51 without
> + * conflicting with the page offset bits.
> + *
> + * This scheme ensures that the single order bit is always in a higher
> + * position than any bit used by the page offset for that same order,
> + * preventing collisions.
Should explain why it is like this:
This scheme allows storing all the multi-order page sizes in a single
6 level table with a good sharing of lower tables levels for 0 top
address bits. A single algorithm can efficiently process everything.
> + */
> +static unsigned long kho_radix_encode(unsigned long pa, unsigned int order)
pa is phys_addr_t in the kernel, never unsigned long.
If you want to make it all dynamic then this should be phys_addr_t
> +{
> + unsigned long h = 1UL << (BITS_PER_LONG - PAGE_SHIFT - order);
And this BITS_PER_LONG is confused, it is BITS_PER_PHYS_ADDR_T which
may not exist.
Use an enum ORDER_0_LG2 maybe
> + unsigned long l = pa >> (PAGE_SHIFT + order);
>
> + return h | l;
> +}
>
> +static unsigned long kho_radix_decode(unsigned long encoded, unsigned int *order)
Returns phys_addr_t
> {
> - void *elm, *res;
> + unsigned long order_bit = fls64(encoded);
unsigned int
> + unsigned long pa;
phys_addr_t
> + *order = BITS_PER_LONG - PAGE_SHIFT - order_bit + 1;
ORDER_0_LG2
> + pa = encoded << (PAGE_SHIFT + *order);
I'd add a comment that the shift always discards order.
> + return pa;
> +}
>
> +static unsigned long kho_radix_get_index(unsigned long encoded, int level)
unsigned int level
> +{
> + int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
> + int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
Stick all the constants that kho_radix_tree_max_depth() are computing
in an enum instead of recomputing them..
> + unsigned long mask;
> + int s;
unsigned for all of these.
> +
> + if (level == 1) {
I think the math is easier if level 0 == bitmap..
> + s = 0;
> + mask = (1UL << bitmap_bit_num) - 1;
> + } else {
> + s = ((level - 2) * table_bit_num) + bitmap_bit_num;
eg here you are doing level-2 which is a bit weird only because of the
arbitary choice to make level=1 be the bitmap.
I'd also use some different names
table_bit_num == TABLE_SIZE_LG2
BITMAP_BIT_NUM = BITMAP_SIZE_LG2
Log2 designates the value is 1<<LG2
> + mask = (1UL << table_bit_num) - 1;
> }
>
> - return elm;
> + return (encoded >> s) & mask;
It is just:
return encoded % (1 << BITMAP_SIZE_LG2);
return (encoded >> s) % (1 << TABLE_SIZE_LG2);
The compiler is smart enough to choose bit logic if that is the
fastest option and the above is more readable.
> +static int kho_radix_set_bitmap(struct kho_bitmap_table *bit_tlb, unsigned long offset)
> {
> + if (!bit_tlb ||
> + offset >= PAGE_SIZE * BITS_PER_BYTE)
> + return -EINVAL;
>
> + set_bit(offset, bit_tlb->bitmaps);
set_bit is an atomic, you want __set_bit()
> + return 0;
> +}
>
> +static int kho_radix_preserve_page(unsigned long pa, unsigned int order)
phys_addr_t
> +{
> + unsigned long encoded = kho_radix_encode(pa, order);
> + int num_tree_level = kho_radix_tree_max_depth();
kho_radix_tree_max_depth() is constant, stick it in an enum with the
rest of them.
> + struct kho_radix_tree *current_tree, *new_tree;
> + struct kho_bitmap_table *bitmap_table;
> + int err = 0;
> + int i, idx;
various unsigned int.
>
> + down_write(&kho_radix_tree_root_sem);
>
> + current_tree = kho_radix_tree_root;
>
> + /* Go from high levels to low levels */
> + for (i = num_tree_level; i >= 1; i--) {
> + idx = kho_radix_get_index(encoded, i);
> +
> + if (i == 1) {
> + bitmap_table = (struct kho_bitmap_table *)current_tree;
> + err = kho_radix_set_bitmap(bitmap_table, idx);
> + goto out;
> + }
> +
> + if (!current_tree->table[idx]) {
> + new_tree = kho_alloc_radix_tree();
> + if (!new_tree) {
> + err = -ENOMEM;
> + goto out;
> + }
> +
> + current_tree->table[idx] =
> + (unsigned long)virt_to_phys(new_tree);
current_tree = new_tree
> + }
else
> +
> + current_tree = (struct kho_radix_tree *)
> + phys_to_virt(current_tree->table[idx]);
> }
> +
> +out:
> + up_write(&kho_radix_tree_root_sem);
> + return err;
> }
>
> +static int kho_radix_walk_bitmaps(struct kho_bitmap_table *bit_tlb,
> + unsigned long offset,
phys_addr_t
> + kho_radix_tree_walk_callback_t cb)
> {
> + unsigned long encoded = offset << (PAGE_SHIFT + ilog2(BITS_PER_BYTE));
> + unsigned long *bitmap = (unsigned long *)bit_tlb;
> + int err = 0;
> + int i;
>
> + for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
> + err = cb(encoded | i);
> + if (err)
> + return err;
> + }
>
> + return 0;
> +}
>
> +static int kho_radix_walk_trees(struct kho_radix_tree *root, int level,
unsigned int
> + unsigned long offset,
phys_addr_t. I would call this start not offset..
> + kho_radix_tree_walk_callback_t cb)
> +{
> + int level_shift = ilog2(PAGE_SIZE / sizeof(unsigned long));
> + struct kho_radix_tree *next_tree;
> + unsigned long encoded, i;
> + int err = 0;
>
> + if (level == 1) {
> + encoded = offset;
> + return kho_radix_walk_bitmaps((struct kho_bitmap_table *)root,
> + encoded, cb);
Better to do this in the caller a few lines below
> + }
>
> + for (i = 0; i < PAGE_SIZE / sizeof(unsigned long); i++) {
> + if (root->table[i]) {
> + encoded = offset << level_shift | i;
This doesn't seem right..
The argument to the walker should be the starting encoded of the table
it is about to walk.
Since everything always starts at 0 it should always be
start | (i << level_shift)
?
> + next_tree = (struct kho_radix_tree *)
> + phys_to_virt(root->table[i]);
> + err = kho_radix_walk_trees(next_tree, level - 1, encoded, cb);
> if (err)
> return err;
> }
> }
>
> + return 0;
> +}
>
> +static int kho_memblock_reserve(phys_addr_t pa, int order)
> +{
> + int sz = 1 << (order + PAGE_SHIFT);
> + struct page *page = phys_to_page(pa);
> +
> + memblock_reserve(pa, sz);
> + memblock_reserved_mark_noinit(pa, sz);
> + page->private = order;
>
> return 0;
> }
>
> +static int kho_radix_walk_trees_callback(unsigned long encoded)
> +{
> + unsigned int order;
> + unsigned long pa;
> +
> + pa = kho_radix_decode(encoded, &order);
> +
> + return kho_memblock_reserve(pa, order);
> +}
> +
> +struct kho_serialization {
> + struct page *fdt;
> + struct list_head fdt_list;
> + struct dentry *sub_fdt_dir;
> +};
> +
> +static int __kho_preserve_order(unsigned long pfn, unsigned int order)
> +{
> + unsigned long pa = PFN_PHYS(pfn);
phys_addr_t
Jason
Hi Jason,
Thank you very much for your feedback again.
On Mon, Oct 6, 2025 at 7:14 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
> > #define KHO_FDT_COMPATIBLE "kho-v1"
>
> We don't bump this?
Will do. Will be "kho-v2".
>
> > -#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
> > +#define PROP_PRESERVED_PAGE_RADIX_TREE "preserved-page-radix-tree"
> > #define PROP_SUB_FDT "fdt"
>
> I'de really like to see all of these sorts of definitions in some
> structured ABI header not open coded all over the place..
Do you think `include/linux/kexec_handover.h` is the appropriate
place, or would you prefer a new, dedicated ABI header (e.g., in
`include/uapi/linux/`) for all KHO-related FDT constants?
>
> > */
> > +struct kho_radix_tree {
> > + unsigned long table[PAGE_SIZE / sizeof(unsigned long)];
>
> This should be phys_addr_t.
>
> > +};
>
> You dropped the macros so now we don't know these are actually
> pointers to 'struct kho_radix_tree'
>
Agreed. Will change `u64` according to Pasha's comment. And we use
explicit casts like `(u64)virt_to_phys(new_tree)` and `(struct
kho_radix_tree *)phys_to_virt(table_entry)` in the current series. I
believe this, along with the `u64` type, makes it clear that the table
stores physical addresses.
> > +static int kho_radix_tree_max_depth(void)
> > +{
> > + int page_offset_bit_num = BITS_PER_LONG - PAGE_SHIFT;
> > + int order_bit_num = ilog2(__roundup_pow_of_two(page_offset_bit_num));
> > + int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
> > + int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > + int table_level_num = DIV_ROUND_UP(page_offset_bit_num -
> > + bitmap_bit_num + order_bit_num,
> > + table_bit_num);
>
> All should be unsigned int. Below I suggest to put it in an enum and
> use different names.. And since the function is constant it can just
> be an enum TOP_LEVEL too.
>
Yes I did think of returning a const for `kho_radix_tree_max_depth()`.
I think using enums is a better idea and I can place all above values
as enums.
> > + */
> > +static unsigned long kho_radix_encode(unsigned long pa, unsigned int order)
>
> pa is phys_addr_t in the kernel, never unsigned long.
>
> If you want to make it all dynamic then this should be phys_addr_t
Should this also be `u64`, or we stay with `phys_addr_t` for all page
addresses?
>
> > +{
> > + unsigned long h = 1UL << (BITS_PER_LONG - PAGE_SHIFT - order);
>
> And this BITS_PER_LONG is confused, it is BITS_PER_PHYS_ADDR_T which
> may not exist.
>
> Use an enum ORDER_0_LG2 maybe
I prefer `KHO_RADIX_ORDER_0_BIT_POS` (defined as `BITS_PER_LONG -
PAGE_SHIFT`) over `ORDER_0_LG2`, as I think the latter is a bit hard
to understand, what do you think? This constant, along with others,
will be placed in the enum.
>
> > + unsigned long l = pa >> (PAGE_SHIFT + order);
> >
> > + return h | l;
> > +}
> >
> > +static unsigned long kho_radix_decode(unsigned long encoded, unsigned int *order)
>
> Returns phys_addr_t
>
> > {
> > - void *elm, *res;
> > + unsigned long order_bit = fls64(encoded);
>
> unsigned int
>
> > + unsigned long pa;
>
> phys_addr_t
>
> > + *order = BITS_PER_LONG - PAGE_SHIFT - order_bit + 1;
>
> ORDER_0_LG2
>
> > + pa = encoded << (PAGE_SHIFT + *order);
>
> I'd add a comment that the shift always discards order.
>
> > + return pa;
> > +}
> >
> > +static unsigned long kho_radix_get_index(unsigned long encoded, int level)
>
> unsigned int level
>
> > +{
> > + int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > + int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
>
> Stick all the constants that kho_radix_tree_max_depth() are computing
> in an enum instead of recomputing them..
>
> > + unsigned long mask;
> > + int s;
>
> unsigned for all of these.
>
> > +
> > + if (level == 1) {
>
> I think the math is easier if level 0 == bitmap..
>
> > + s = 0;
> > + mask = (1UL << bitmap_bit_num) - 1;
> > + } else {
> > + s = ((level - 2) * table_bit_num) + bitmap_bit_num;
>
> eg here you are doing level-2 which is a bit weird only because of the
> arbitary choice to make level=1 be the bitmap.
>
> I'd also use some different names
>
> table_bit_num == TABLE_SIZE_LG2
> BITMAP_BIT_NUM = BITMAP_SIZE_LG2
>
> Log2 designates the value is 1<<LG2
Good point on the level numbering, we'll switch to 0-based where level
0 is the bitmap. The modulo operations you suggested play nicely with
the 0-based numbering too, thanks. Will also update the names and put
them in enum.
>
> > + mask = (1UL << table_bit_num) - 1;
> > }
> >
> > - return elm;
> > + return (encoded >> s) & mask;
>
> It is just:
>
> return encoded % (1 << BITMAP_SIZE_LG2);
> return (encoded >> s) % (1 << TABLE_SIZE_LG2);
>
> The compiler is smart enough to choose bit logic if that is the
> fastest option and the above is more readable.
>
> > +static int kho_radix_set_bitmap(struct kho_bitmap_table *bit_tlb, unsigned long offset)
> > {
> > + if (!bit_tlb ||
> > + offset >= PAGE_SIZE * BITS_PER_BYTE)
> > + return -EINVAL;
> >
> > + set_bit(offset, bit_tlb->bitmaps);
>
> set_bit is an atomic, you want __set_bit()
>
> > + return 0;
> > +}
> >
> > +static int kho_radix_preserve_page(unsigned long pa, unsigned int order)
>
> phys_addr_t
>
> > +{
> > + unsigned long encoded = kho_radix_encode(pa, order);
> > + int num_tree_level = kho_radix_tree_max_depth();
>
> kho_radix_tree_max_depth() is constant, stick it in an enum with the
> rest of them.
>
> > + struct kho_radix_tree *current_tree, *new_tree;
> > + struct kho_bitmap_table *bitmap_table;
> > + int err = 0;
> > + int i, idx;
>
> various unsigned int.
>
> >
> > + down_write(&kho_radix_tree_root_sem);
> >
> > + current_tree = kho_radix_tree_root;
> >
> > + /* Go from high levels to low levels */
> > + for (i = num_tree_level; i >= 1; i--) {
> > + idx = kho_radix_get_index(encoded, i);
> > +
> > + if (i == 1) {
> > + bitmap_table = (struct kho_bitmap_table *)current_tree;
> > + err = kho_radix_set_bitmap(bitmap_table, idx);
> > + goto out;
> > + }
> > +
> > + if (!current_tree->table[idx]) {
> > + new_tree = kho_alloc_radix_tree();
> > + if (!new_tree) {
> > + err = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + current_tree->table[idx] =
> > + (unsigned long)virt_to_phys(new_tree);
>
> current_tree = new_tree
> > + }
>
> else
>
> > +
> > + current_tree = (struct kho_radix_tree *)
> > + phys_to_virt(current_tree->table[idx]);
> > }
> > +
> > +out:
> > + up_write(&kho_radix_tree_root_sem);
> > + return err;
> > }
> >
> > +static int kho_radix_walk_bitmaps(struct kho_bitmap_table *bit_tlb,
> > + unsigned long offset,
>
> phys_addr_t
>
> > + kho_radix_tree_walk_callback_t cb)
> > {
> > + unsigned long encoded = offset << (PAGE_SHIFT + ilog2(BITS_PER_BYTE));
> > + unsigned long *bitmap = (unsigned long *)bit_tlb;
> > + int err = 0;
> > + int i;
> >
> > + for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
> > + err = cb(encoded | i);
> > + if (err)
> > + return err;
> > + }
> >
> > + return 0;
> > +}
> >
> > +static int kho_radix_walk_trees(struct kho_radix_tree *root, int level,
>
> unsigned int
>
> > + unsigned long offset,
>
> phys_addr_t. I would call this start not offset..
>
> > + kho_radix_tree_walk_callback_t cb)
> > +{
> > + int level_shift = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > + struct kho_radix_tree *next_tree;
> > + unsigned long encoded, i;
> > + int err = 0;
> >
> > + if (level == 1) {
> > + encoded = offset;
> > + return kho_radix_walk_bitmaps((struct kho_bitmap_table *)root,
> > + encoded, cb);
>
> Better to do this in the caller a few lines below
But the caller is in a different tree level? Should we only walk the
bitmaps at the lowest level?
>
> > + }
>
> >
> > + for (i = 0; i < PAGE_SIZE / sizeof(unsigned long); i++) {
> > + if (root->table[i]) {
> > + encoded = offset << level_shift | i;
>
> This doesn't seem right..
>
> The argument to the walker should be the starting encoded of the table
> it is about to walk.
>
> Since everything always starts at 0 it should always be
> start | (i << level_shift)
>
> ?
You're right that this line might not be immediately intuitive. The
var `level_shift` (which is constant value 9 here) is applied to the
*accumulated* `offset` from the parent level. Let's consider an
example of a preserved page at physical address `0x1000`, which
encodes to `0x10000000000001` (bit 52 is set for order 0, bit 0 is set
for page 1).
If we were to use `start | (i << level_shift)` where `level_shift` is
a constant 9, and `start` is the value from the parent call:
- At Level 6, `start` is `0`. `i` is 2 as bit 51:59 = 2. Result: `0
| (2 << 9) = 0x400`. This is passed to Level 5.
- At Level 5, `start` is `0x400`, `i` is 0 as bit 50:42 = 0. Result:
`0x400 | (0 << 9) = 0x400`. This is passed to Level 4.
- At Level 4, `start` is `0x400`, `i` is 0 as bit 33:41 = 0. Result:
`0x400 | (0 << 9) = 0x400`. And so on.
As you can see, the encoded value is not correctly reconstructed. This
will work if the `level_shift` represents the total shift from the LSB
for each specific level, but it is not the case here.
I will, however, add a detailed comment to `kho_radix_walk_trees` to
clarify this logic. I also agree to change the name of `offset` to
make it more clearer, how about `base_encoded`, or do you still prefer
`start`?
>
> > + next_tree = (struct kho_radix_tree *)
> > + phys_to_virt(root->table[i]);
> > + err = kho_radix_walk_trees(next_tree, level - 1, encoded, cb);
> > if (err)
> > return err;
> > }
> > }
> >
> > + return 0;
> > +}
> >
> > +static int kho_memblock_reserve(phys_addr_t pa, int order)
> > +{
> > + int sz = 1 << (order + PAGE_SHIFT);
> > + struct page *page = phys_to_page(pa);
> > +
> > + memblock_reserve(pa, sz);
> > + memblock_reserved_mark_noinit(pa, sz);
> > + page->private = order;
> >
> > return 0;
> > }
> >
> > +static int kho_radix_walk_trees_callback(unsigned long encoded)
> > +{
> > + unsigned int order;
> > + unsigned long pa;
> > +
> > + pa = kho_radix_decode(encoded, &order);
> > +
> > + return kho_memblock_reserve(pa, order);
> > +}
> > +
> > +struct kho_serialization {
> > + struct page *fdt;
> > + struct list_head fdt_list;
> > + struct dentry *sub_fdt_dir;
> > +};
> > +
> > +static int __kho_preserve_order(unsigned long pfn, unsigned int order)
> > +{
> > + unsigned long pa = PFN_PHYS(pfn);
>
> phys_addr_t
>
> Jason
Will do the update in the next patch version. Thanks again.
--
Jason Miu
> > > -#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
> > > +#define PROP_PRESERVED_PAGE_RADIX_TREE "preserved-page-radix-tree"
> > > #define PROP_SUB_FDT "fdt"
> >
> > I'de really like to see all of these sorts of definitions in some
> > structured ABI header not open coded all over the place..
>
> Do you think `include/linux/kexec_handover.h` is the appropriate
> place, or would you prefer a new, dedicated ABI header (e.g., in
> `include/uapi/linux/`) for all KHO-related FDT constants?
I would avoid uapi, but maybe Pasha has some
idea.
include/linux/live_update/abi/ ?
> Agreed. Will change `u64` according to Pasha's comment. And we use
> explicit casts like `(u64)virt_to_phys(new_tree)` and `(struct
> kho_radix_tree *)phys_to_virt(table_entry)` in the current series. I
> believe this, along with the `u64` type, makes it clear that the table
> stores physical addresses.
Well, the macros were intended to automate this and avoid mistakes
from opencoding.. Just keep using them?
> > > + */
> > > +static unsigned long kho_radix_encode(unsigned long pa, unsigned int order)
> >
> > pa is phys_addr_t in the kernel, never unsigned long.
> >
> > If you want to make it all dynamic then this should be phys_addr_t
>
> Should this also be `u64`, or we stay with `phys_addr_t` for all page
> addresses?
you should use phys_addr_t for everything that originates from a
phys_addr_t, and u64 for all the ABI
> > > +{
> > > + unsigned long h = 1UL << (BITS_PER_LONG - PAGE_SHIFT - order);
> >
> > And this BITS_PER_LONG is confused, it is BITS_PER_PHYS_ADDR_T which
> > may not exist.
> >
> > Use an enum ORDER_0_LG2 maybe
>
> I prefer `KHO_RADIX_ORDER_0_BIT_POS` (defined as `BITS_PER_LONG -
> PAGE_SHIFT`) over `ORDER_0_LG2`, as I think the latter is a bit hard
> to understand, what do you think? This constant, along with others,
> will be placed in the enum.
Sure, though I prefer LG2 to BIT_POS
BIT_POS to me implies it is being used as bit wise operation, while
log2 is a mathematical concept
X_lg2 = ilog2(X) && X == 1 << X_lg2
> > > + kho_radix_tree_walk_callback_t cb)
> > > +{
> > > + int level_shift = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > > + struct kho_radix_tree *next_tree;
> > > + unsigned long encoded, i;
> > > + int err = 0;
> > >
> > > + if (level == 1) {
> > > + encoded = offset;
> > > + return kho_radix_walk_bitmaps((struct kho_bitmap_table *)root,
> > > + encoded, cb);
> >
> > Better to do this in the caller a few lines below
>
> But the caller is in a different tree level? Should we only walk the
> bitmaps at the lowest level?
I mean just have the caller do
if (level-1 ==0)
kho_radix_walk_bitmaps()
else
..
Avoids a function call
> > > + for (i = 0; i < PAGE_SIZE / sizeof(unsigned long); i++) {
> > > + if (root->table[i]) {
> > > + encoded = offset << level_shift | i;
> >
> > This doesn't seem right..
> >
> > The argument to the walker should be the starting encoded of the table
> > it is about to walk.
> >
> > Since everything always starts at 0 it should always be
> > start | (i << level_shift)
> >
> > ?
>
> You're right that this line might not be immediately intuitive. The
> var `level_shift` (which is constant value 9 here) is applied to the
> *accumulated* `offset` from the parent level. Let's consider an
> example of a preserved page at physical address `0x1000`, which
> encodes to `0x10000000000001` (bit 52 is set for order 0, bit 0 is set
> for page 1).
Oh, weird, too weird maybe. I'd just keep all the values as fully
shifted, level_shift should be adjusted to have the full shift for
this level. Easier to understand.
Also, I think the order bits might have become a bit confused, I think
I explained it wrong.
My idea was to try to share the radix levels to save space eg if we
have like this patch does:
Order phys
00001 abcd
00010 0bcd
00100 00cd
01000 000d
Then we don't get too much page level sharing, the middle ends up with
0 indexes in tables that cannot be shared.
What I was going for was to push all the shared pages to the left
00001 abcd
00000 1bcd
00000 01cd
00000 001d
Here the first radix level has index 0 or 1 and is fully shared. So eg
Order 4 and 5 will have all the same 0 index table levels. This also
reduces the max height of the tree because only +1 bit is needed to
store order.
Jason
Thanks Jason, I uploaded the patch v2 according to your feedback.
On Thu, Oct 9, 2025 at 10:52 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> > > > -#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
> > > > +#define PROP_PRESERVED_PAGE_RADIX_TREE "preserved-page-radix-tree"
> > > > #define PROP_SUB_FDT "fdt"
> > >
> > > I'de really like to see all of these sorts of definitions in some
> > > structured ABI header not open coded all over the place..
> >
> > Do you think `include/linux/kexec_handover.h` is the appropriate
> > place, or would you prefer a new, dedicated ABI header (e.g., in
> > `include/uapi/linux/`) for all KHO-related FDT constants?
>
> I would avoid uapi, but maybe Pasha has some
> idea.
>
> include/linux/live_update/abi/ ?
Yes, moved to include/linux/live_update/abi/.
>
> > Agreed. Will change `u64` according to Pasha's comment. And we use
> > explicit casts like `(u64)virt_to_phys(new_tree)` and `(struct
> > kho_radix_tree *)phys_to_virt(table_entry)` in the current series. I
> > believe this, along with the `u64` type, makes it clear that the table
> > stores physical addresses.
>
> Well, the macros were intended to automate this and avoid mistakes
> from opencoding.. Just keep using them?
>
Sure, added two inline functions `kho_radix_tree_desc()` and
`kho_radix_tree()` back for converting.
> > > > + */
> > > > +static unsigned long kho_radix_encode(unsigned long pa, unsigned int order)
> > >
> > > pa is phys_addr_t in the kernel, never unsigned long.
> > >
> > > If you want to make it all dynamic then this should be phys_addr_t
> >
> > Should this also be `u64`, or we stay with `phys_addr_t` for all page
> > addresses?
>
> you should use phys_addr_t for everything that originates from a
> phys_addr_t, and u64 for all the ABI
>
done
> > > > +{
> > > > + unsigned long h = 1UL << (BITS_PER_LONG - PAGE_SHIFT - order);
> > >
> > > And this BITS_PER_LONG is confused, it is BITS_PER_PHYS_ADDR_T which
> > > may not exist.
> > >
> > > Use an enum ORDER_0_LG2 maybe
> >
> > I prefer `KHO_RADIX_ORDER_0_BIT_POS` (defined as `BITS_PER_LONG -
> > PAGE_SHIFT`) over `ORDER_0_LG2`, as I think the latter is a bit hard
> > to understand, what do you think? This constant, along with others,
> > will be placed in the enum.
>
> Sure, though I prefer LG2 to BIT_POS
Lets pick LG2. =)
>
> BIT_POS to me implies it is being used as bit wise operation, while
> log2 is a mathematical concept
>
> X_lg2 = ilog2(X) && X == 1 << X_lg2
>
> > > > + kho_radix_tree_walk_callback_t cb)
> > > > +{
> > > > + int level_shift = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > > > + struct kho_radix_tree *next_tree;
> > > > + unsigned long encoded, i;
> > > > + int err = 0;
> > > >
> > > > + if (level == 1) {
> > > > + encoded = offset;
> > > > + return kho_radix_walk_bitmaps((struct kho_bitmap_table *)root,
> > > > + encoded, cb);
> > >
> > > Better to do this in the caller a few lines below
> >
> > But the caller is in a different tree level? Should we only walk the
> > bitmaps at the lowest level?
>
> I mean just have the caller do
>
> if (level-1 ==0)
> kho_radix_walk_bitmaps()
> else
> ..
>
> Avoids a function call
I see. Done.
>
> > > > + for (i = 0; i < PAGE_SIZE / sizeof(unsigned long); i++) {
> > > > + if (root->table[i]) {
> > > > + encoded = offset << level_shift | i;
> > >
> > > This doesn't seem right..
> > >
> > > The argument to the walker should be the starting encoded of the table
> > > it is about to walk.
> > >
> > > Since everything always starts at 0 it should always be
> > > start | (i << level_shift)
> > >
> > > ?
> >
> > You're right that this line might not be immediately intuitive. The
> > var `level_shift` (which is constant value 9 here) is applied to the
> > *accumulated* `offset` from the parent level. Let's consider an
> > example of a preserved page at physical address `0x1000`, which
> > encodes to `0x10000000000001` (bit 52 is set for order 0, bit 0 is set
> > for page 1).
>
> Oh, weird, too weird maybe. I'd just keep all the values as fully
> shifted, level_shift should be adjusted to have the full shift for
> this level. Easier to understand.
>
> Also, I think the order bits might have become a bit confused, I think
> I explained it wrong.
>
> My idea was to try to share the radix levels to save space eg if we
> have like this patch does:
>
> Order phys
> 00001 abcd
> 00010 0bcd
> 00100 00cd
> 01000 000d
>
> Then we don't get too much page level sharing, the middle ends up with
> 0 indexes in tables that cannot be shared.
>
> What I was going for was to push all the shared pages to the left
>
> 00001 abcd
> 00000 1bcd
> 00000 01cd
> 00000 001d
>
> Here the first radix level has index 0 or 1 and is fully shared. So eg
> Order 4 and 5 will have all the same 0 index table levels. This also
> reduces the max height of the tree because only +1 bit is needed to
> store order.
>
> Jason
Thanks for the clarification. I updated the logic by keeping the
encoded value fully shifted and adjusting the `level_shift` according
to the current level.
And yes we are having the shared pages on the left side (zeros in the
encoded prefix) while having the order bits shift to right when the
page order increases. I hope the updated code makes this more clearer.
--
Jason Miu
On Mon, Oct 6, 2025 at 10:14 AM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> On Tue, Sep 30, 2025 at 06:19:39PM -0700, Jason Miu wrote:
> > @@ -29,7 +30,7 @@
> > #include "kexec_internal.h"
> >
> > #define KHO_FDT_COMPATIBLE "kho-v1"
>
> We don't bump this?
>
> > -#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"
> > +#define PROP_PRESERVED_PAGE_RADIX_TREE "preserved-page-radix-tree"
> > #define PROP_SUB_FDT "fdt"
>
> I'de really like to see all of these sorts of definitions in some
> structured ABI header not open coded all over the place..
>
> > /*
> > + * The KHO radix tree tracks preserved memory pages. It is a hierarchical
> > + * structure that starts with a single root `kho_radix_tree`. This single
> > + * tree stores pages of all orders.
> > + *
> > + * This is achieved by encoding the page's physical address and its order into
> > + * a single `unsigned long` value. This encoded value is then used to traverse
> > + * the tree.
> > + *
> > + * The tree hierarchy is shown below:
> > + *
> > + * kho_radix_tree_root
> > + * +-------------------+
> > + * | Level 6 | (struct kho_radix_tree)
> > + * +-------------------+
> > + * |
> > + * v
> > + * +-------------------+
> > + * | Level 5 | (struct kho_radix_tree)
> > + * +-------------------+
> > + * |
> > + * | ... (intermediate levels)
> > + * |
> > + * v
> > + * +-------------------+
> > + * | Level 1 | (struct kho_bitmap_table)
> > + * +-------------------+
> > + *
> > + * The following diagram illustrates how the encoded value is split into
> > + * indices for the tree levels:
> > *
> > + * 63:60 59:51 50:42 41:33 32:24 23:15 14:0
> > + * +---------+--------+--------+--------+--------+--------+-----------------+
> > + * | 0 | Lv 6 | Lv 5 | Lv 4 | Lv 3 | Lv 2 | Lv 1 (bitmap) |
> > + * +---------+--------+--------+--------+--------+--------+-----------------+
> > *
> > + * Each `kho_radix_tree` (Levels 2-6) and `kho_bitmap_table` (Level 1) is
> > + * PAGE_SIZE. Each entry in a `kho_radix_tree` is a descriptor (a physical
> > + * address) pointing to the next level node. For Level 2 `kho_radix_tree`
> > + * nodes, these descriptors point to a `kho_bitmap_table`. The final
> > + * `kho_bitmap_table` is a bitmap where each set bit represents a single
> > + * preserved page.
>
> Maybe a note that this is example is for PAGE_SIZE=4k.
>
>
> > */
> > +struct kho_radix_tree {
> > + unsigned long table[PAGE_SIZE / sizeof(unsigned long)];
>
> This should be phys_addr_t.
Maybe u64 ? This is a preserved data, I would specify the size, and
not care about 32-bit arches. Also, if we ever have to support larger
physical spaces, this radix tree version would need to be bumped
anyway.
>
> > +};
>
> You dropped the macros so now we don't know these are actually
> pointers to 'struct kho_radix_tree'
>
> > +/*
> > + * `kho_radix_tree_root` points to a page thats serves as the root of the
> > + * KHO radix tree. This page is allocated during KHO module initialization.
> > + * Its physical address is written to the FDT and passed to the next kernel
> > + * during kexec.
> > + */
> > +static struct kho_radix_tree *kho_radix_tree_root;
> > +static DECLARE_RWSEM(kho_radix_tree_root_sem);
> > +
> > +static int kho_radix_tree_max_depth(void)
> > +{
> > + int page_offset_bit_num = BITS_PER_LONG - PAGE_SHIFT;
> > + int order_bit_num = ilog2(__roundup_pow_of_two(page_offset_bit_num));
> > + int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
> > + int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > + int table_level_num = DIV_ROUND_UP(page_offset_bit_num -
> > + bitmap_bit_num + order_bit_num,
> > + table_bit_num);
>
> All should be unsigned int. Below I suggest to put it in an enum and
> use different names.. And since the function is constant it can just
> be an enum TOP_LEVEL too.
>
> > +/*
> > + * The KHO radix tree tracks preserved pages by encoding a page's physical
> > + * address (pa) and its order into a single unsigned long value. This value
> > + * is then used to traverse the tree. The encoded value is composed of two
> > + * parts: the 'order bits' in the upper part and the 'page offset' in the
> > + * lower part.
> > + *
> > + * <-- Higher Bits ------------------------------------ Lower Bits -->
> > + * +--------------------------+-----------------------------------------+
> > + * | Order Bits | Page Offset |
> > + * +--------------------------+-----------------------------------------+
> > + * | ... 0 0 1 0 0 ... | pa >> (PAGE_SHIFT + order) |
> > + * +--------------------------+-----------------------------------------+
> > + * ^
> > + * |
> > + * This single '1' bit's position
> > + * uniquely identifies the 'order'.
> > + *
> > + *
> > + * Page Offset:
> > + * The 'page offset' is the physical address normalized for its order. It
> > + * effectively represents the page offset for the given order.
> > + *
> > + * Order Bits:
> > + * The 'order bits' encode the page order by setting a single bit at a
> > + * specific position. The position of this bit itself represents the order.
> > + *
> > + * For instance, on a 64-bit system with 4KB pages (PAGE_SHIFT = 12), the
> > + * maximum range for a page offset (for order 0) is 52 bits (64 - 12). This
> > + * offset occupies bits [0-51]. For order 0, the order bit is set at
> > + * position 52.
> > + *
> > + * As the order increases, the number of bits required for the 'page offset'
> > + * decreases. For example, order 1 requires one less bit for its page
> > + * offset. This allows its order bit to be set at position 51 without
> > + * conflicting with the page offset bits.
> > + *
> > + * This scheme ensures that the single order bit is always in a higher
> > + * position than any bit used by the page offset for that same order,
> > + * preventing collisions.
>
> Should explain why it is like this:
>
> This scheme allows storing all the multi-order page sizes in a single
> 6 level table with a good sharing of lower tables levels for 0 top
> address bits. A single algorithm can efficiently process everything.
>
> > + */
> > +static unsigned long kho_radix_encode(unsigned long pa, unsigned int order)
>
> pa is phys_addr_t in the kernel, never unsigned long.
>
> If you want to make it all dynamic then this should be phys_addr_t
>
> > +{
> > + unsigned long h = 1UL << (BITS_PER_LONG - PAGE_SHIFT - order);
>
> And this BITS_PER_LONG is confused, it is BITS_PER_PHYS_ADDR_T which
> may not exist.
>
> Use an enum ORDER_0_LG2 maybe
>
> > + unsigned long l = pa >> (PAGE_SHIFT + order);
> >
> > + return h | l;
> > +}
> >
> > +static unsigned long kho_radix_decode(unsigned long encoded, unsigned int *order)
>
> Returns phys_addr_t
>
> > {
> > - void *elm, *res;
> > + unsigned long order_bit = fls64(encoded);
>
> unsigned int
>
> > + unsigned long pa;
>
> phys_addr_t
>
> > + *order = BITS_PER_LONG - PAGE_SHIFT - order_bit + 1;
>
> ORDER_0_LG2
>
> > + pa = encoded << (PAGE_SHIFT + *order);
>
> I'd add a comment that the shift always discards order.
>
> > + return pa;
> > +}
> >
> > +static unsigned long kho_radix_get_index(unsigned long encoded, int level)
>
> unsigned int level
>
> > +{
> > + int table_bit_num = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > + int bitmap_bit_num = PAGE_SHIFT + ilog2(BITS_PER_BYTE);
>
> Stick all the constants that kho_radix_tree_max_depth() are computing
> in an enum instead of recomputing them..
>
> > + unsigned long mask;
> > + int s;
>
> unsigned for all of these.
>
> > +
> > + if (level == 1) {
>
> I think the math is easier if level 0 == bitmap..
>
> > + s = 0;
> > + mask = (1UL << bitmap_bit_num) - 1;
> > + } else {
> > + s = ((level - 2) * table_bit_num) + bitmap_bit_num;
>
> eg here you are doing level-2 which is a bit weird only because of the
> arbitary choice to make level=1 be the bitmap.
>
> I'd also use some different names
>
> table_bit_num == TABLE_SIZE_LG2
> BITMAP_BIT_NUM = BITMAP_SIZE_LG2
>
> Log2 designates the value is 1<<LG2
>
> > + mask = (1UL << table_bit_num) - 1;
> > }
> >
> > - return elm;
> > + return (encoded >> s) & mask;
>
> It is just:
>
> return encoded % (1 << BITMAP_SIZE_LG2);
> return (encoded >> s) % (1 << TABLE_SIZE_LG2);
>
> The compiler is smart enough to choose bit logic if that is the
> fastest option and the above is more readable.
>
> > +static int kho_radix_set_bitmap(struct kho_bitmap_table *bit_tlb, unsigned long offset)
> > {
> > + if (!bit_tlb ||
> > + offset >= PAGE_SIZE * BITS_PER_BYTE)
> > + return -EINVAL;
> >
> > + set_bit(offset, bit_tlb->bitmaps);
>
> set_bit is an atomic, you want __set_bit()
>
> > + return 0;
> > +}
> >
> > +static int kho_radix_preserve_page(unsigned long pa, unsigned int order)
>
> phys_addr_t
>
> > +{
> > + unsigned long encoded = kho_radix_encode(pa, order);
> > + int num_tree_level = kho_radix_tree_max_depth();
>
> kho_radix_tree_max_depth() is constant, stick it in an enum with the
> rest of them.
>
> > + struct kho_radix_tree *current_tree, *new_tree;
> > + struct kho_bitmap_table *bitmap_table;
> > + int err = 0;
> > + int i, idx;
>
> various unsigned int.
>
> >
> > + down_write(&kho_radix_tree_root_sem);
> >
> > + current_tree = kho_radix_tree_root;
> >
> > + /* Go from high levels to low levels */
> > + for (i = num_tree_level; i >= 1; i--) {
> > + idx = kho_radix_get_index(encoded, i);
> > +
> > + if (i == 1) {
> > + bitmap_table = (struct kho_bitmap_table *)current_tree;
> > + err = kho_radix_set_bitmap(bitmap_table, idx);
> > + goto out;
> > + }
> > +
> > + if (!current_tree->table[idx]) {
> > + new_tree = kho_alloc_radix_tree();
> > + if (!new_tree) {
> > + err = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + current_tree->table[idx] =
> > + (unsigned long)virt_to_phys(new_tree);
>
> current_tree = new_tree
> > + }
>
> else
>
> > +
> > + current_tree = (struct kho_radix_tree *)
> > + phys_to_virt(current_tree->table[idx]);
> > }
> > +
> > +out:
> > + up_write(&kho_radix_tree_root_sem);
> > + return err;
> > }
> >
> > +static int kho_radix_walk_bitmaps(struct kho_bitmap_table *bit_tlb,
> > + unsigned long offset,
>
> phys_addr_t
>
> > + kho_radix_tree_walk_callback_t cb)
> > {
> > + unsigned long encoded = offset << (PAGE_SHIFT + ilog2(BITS_PER_BYTE));
> > + unsigned long *bitmap = (unsigned long *)bit_tlb;
> > + int err = 0;
> > + int i;
> >
> > + for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
> > + err = cb(encoded | i);
> > + if (err)
> > + return err;
> > + }
> >
> > + return 0;
> > +}
> >
> > +static int kho_radix_walk_trees(struct kho_radix_tree *root, int level,
>
> unsigned int
>
> > + unsigned long offset,
>
> phys_addr_t. I would call this start not offset..
>
> > + kho_radix_tree_walk_callback_t cb)
> > +{
> > + int level_shift = ilog2(PAGE_SIZE / sizeof(unsigned long));
> > + struct kho_radix_tree *next_tree;
> > + unsigned long encoded, i;
> > + int err = 0;
> >
> > + if (level == 1) {
> > + encoded = offset;
> > + return kho_radix_walk_bitmaps((struct kho_bitmap_table *)root,
> > + encoded, cb);
>
> Better to do this in the caller a few lines below
>
> > + }
>
> >
> > + for (i = 0; i < PAGE_SIZE / sizeof(unsigned long); i++) {
> > + if (root->table[i]) {
> > + encoded = offset << level_shift | i;
>
> This doesn't seem right..
>
> The argument to the walker should be the starting encoded of the table
> it is about to walk.
>
> Since everything always starts at 0 it should always be
> start | (i << level_shift)
>
> ?
>
> > + next_tree = (struct kho_radix_tree *)
> > + phys_to_virt(root->table[i]);
> > + err = kho_radix_walk_trees(next_tree, level - 1, encoded, cb);
> > if (err)
> > return err;
> > }
> > }
> >
> > + return 0;
> > +}
> >
> > +static int kho_memblock_reserve(phys_addr_t pa, int order)
> > +{
> > + int sz = 1 << (order + PAGE_SHIFT);
> > + struct page *page = phys_to_page(pa);
> > +
> > + memblock_reserve(pa, sz);
> > + memblock_reserved_mark_noinit(pa, sz);
> > + page->private = order;
> >
> > return 0;
> > }
> >
> > +static int kho_radix_walk_trees_callback(unsigned long encoded)
> > +{
> > + unsigned int order;
> > + unsigned long pa;
> > +
> > + pa = kho_radix_decode(encoded, &order);
> > +
> > + return kho_memblock_reserve(pa, order);
> > +}
> > +
> > +struct kho_serialization {
> > + struct page *fdt;
> > + struct list_head fdt_list;
> > + struct dentry *sub_fdt_dir;
> > +};
> > +
> > +static int __kho_preserve_order(unsigned long pfn, unsigned int order)
> > +{
> > + unsigned long pa = PFN_PHYS(pfn);
>
> phys_addr_t
>
> Jason
On Mon, Oct 06, 2025 at 01:26:57PM -0400, Pasha Tatashin wrote:
> > > +struct kho_radix_tree {
> > > + unsigned long table[PAGE_SIZE / sizeof(unsigned long)];
> >
> > This should be phys_addr_t.
>
> Maybe u64 ? This is a preserved data, I would specify the size, and
> not care about 32-bit arches. Also, if we ever have to support larger
> physical spaces, this radix tree version would need to be bumped
> anyway.
Yeah, that is a good plan.
Jason
Hi Jason, kernel test robot noticed the following build warnings: [auto build test WARNING on rppt-memblock/for-next] [also build test WARNING on linus/master v6.17] [cannot apply to rppt-memblock/fixes akpm-mm/mm-everything next-20250929] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch#_base_tree_information] url: https://github.com/intel-lab-lkp/linux/commits/Jason-Miu/kho-Adopt-KHO-radix-tree-data-structures/20251001-092230 base: https://git.kernel.org/pub/scm/linux/kernel/git/rppt/memblock.git for-next patch link: https://lore.kernel.org/r/20251001011941.1513050-2-jasonmiu%40google.com patch subject: [PATCH v1 1/3] kho: Adopt KHO radix tree data structures config: x86_64-randconfig-005-20251001 (https://download.01.org/0day-ci/archive/20251002/202510021229.mKL5i2Vt-lkp@intel.com/config) compiler: gcc-14 (Debian 14.2.0-19) 14.2.0 reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251002/202510021229.mKL5i2Vt-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202510021229.mKL5i2Vt-lkp@intel.com/ All warnings (new ones prefixed by >>, old ones prefixed by <<): >> WARNING: modpost: vmlinux: section mismatch in reference: kho_radix_walk_trees_callback+0x83 (section: .text) -> __memblock_reserve (section: .init.text) >> WARNING: modpost: vmlinux: section mismatch in reference: kho_radix_walk_trees_callback+0x91 (section: .text) -> memblock_reserved_mark_noinit (section: .init.text) -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests/wiki
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