From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

A vmalloc allocation is preserved using binary structure similar to
global KHO memory tracker. It's a linked list of pages where each page
is an array of physical address of pages in vmalloc area.

kho_preserve_vmalloc() hands out the physical address of the head page
to the caller. This address is used as the argument to
kho_vmalloc_restore() to restore the mapping in the vmalloc address
space and populate it with the preserved pages.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 include/linux/kexec_handover.h |  12 ++
 kernel/kexec_handover.c        | 200 +++++++++++++++++++++++++++++++++
 2 files changed, 212 insertions(+)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 348844cffb13..b7bf3bf11019 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -42,8 +42,10 @@ struct kho_serialization;
 bool kho_is_enabled(void);
 
 int kho_preserve_folio(struct folio *folio);
+int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation);
 int kho_preserve_phys(phys_addr_t phys, size_t size);
 struct folio *kho_restore_folio(phys_addr_t phys);
+void *kho_restore_vmalloc(phys_addr_t preservation);
 int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt);
 int kho_retrieve_subtree(const char *name, phys_addr_t *phys);
 
@@ -70,11 +72,21 @@ static inline int kho_preserve_phys(phys_addr_t phys, size_t size)
 	return -EOPNOTSUPP;
 }
 
+static inline int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline struct folio *kho_restore_folio(phys_addr_t phys)
 {
 	return NULL;
 }
 
+static inline void *kho_restore_vmalloc(phys_addr_t preservation)
+{
+	return NULL;
+}
+
 static inline int kho_add_subtree(struct kho_serialization *ser,
 				  const char *name, void *fdt)
 {
diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index 8079fc4b9189..1177cc5ffa1a 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/vmalloc.h>
 
 #include <asm/early_ioremap.h>
 
@@ -742,6 +743,205 @@ int kho_preserve_phys(phys_addr_t phys, size_t size)
 }
 EXPORT_SYMBOL_GPL(kho_preserve_phys);
 
+struct kho_vmalloc_chunk;
+
+struct kho_vmalloc_hdr {
+	DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *);
+	unsigned int total_pages;	/* only valid in the first chunk */
+	unsigned int flags;		/* only valid in the first chunk */
+	unsigned short order;		/* only valid in the first chunk */
+	unsigned short num_elms;
+};
+
+#define KHO_VMALLOC_SIZE				\
+	((PAGE_SIZE - sizeof(struct kho_vmalloc_hdr)) / \
+	 sizeof(phys_addr_t))
+
+struct kho_vmalloc_chunk {
+	struct kho_vmalloc_hdr hdr;
+	phys_addr_t phys[KHO_VMALLOC_SIZE];
+};
+
+static_assert(sizeof(struct kho_vmalloc_chunk) == PAGE_SIZE);
+
+#define KHO_VMALLOC_FLAGS_MASK	(VM_ALLOC | VM_ALLOW_HUGE_VMAP)
+
+static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)
+{
+	struct kho_vmalloc_chunk *chunk;
+	int err;
+
+	chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!chunk)
+		return NULL;
+
+	err = kho_preserve_phys(virt_to_phys(chunk), PAGE_SIZE);
+	if (err)
+		goto err_free;
+	if (cur)
+		KHOSER_STORE_PTR(cur->hdr.next, chunk);
+	return chunk;
+
+err_free:
+	kfree(chunk);
+	return NULL;
+}
+
+static void kho_vmalloc_free_chunks(struct kho_vmalloc_chunk *first_chunk)
+{
+	struct kho_mem_track *track = &kho_out.ser.track;
+	struct kho_vmalloc_chunk *chunk = first_chunk;
+
+	while (chunk) {
+		unsigned long pfn = PHYS_PFN(virt_to_phys(chunk));
+		struct kho_vmalloc_chunk *tmp = chunk;
+
+		__kho_unpreserve(track, pfn, pfn + 1);
+
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+		kfree(tmp);
+	}
+}
+
+/**
+ * kho_preserve_vmalloc - preserve memory allocated with vmalloc() across kexec
+ * @ptr: pointer to the area in vmalloc address space
+ * @preservation: returned physical address of preservation metadata
+ *
+ * Instructs KHO to preserve the area in vmalloc address space at @ptr. The
+ * physical pages mapped at @ptr will be preserved and on successful return
+ * @preservation will hold the physical address of a structure that describes
+ * the preservation.
+ *
+ * NOTE: The memory allocated with vmalloc_node() variants cannot be reliably
+ * restored on the same node
+ *
+ * Return: 0 on success, error code on failure
+ */
+int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation)
+{
+	struct kho_mem_track *track = &kho_out.ser.track;
+	struct kho_vmalloc_chunk *chunk, *first_chunk;
+	struct vm_struct *vm = find_vm_area(ptr);
+	unsigned int order, flags;
+	int err;
+
+	if (!vm)
+		return -EINVAL;
+
+	if (vm->flags & ~KHO_VMALLOC_FLAGS_MASK)
+		return -EOPNOTSUPP;
+
+	flags = vm->flags & KHO_VMALLOC_FLAGS_MASK;
+	order = get_vm_area_page_order(vm);
+
+	chunk = new_vmalloc_chunk(NULL);
+	if (!chunk)
+		return -ENOMEM;
+	first_chunk = chunk;
+	first_chunk->hdr.total_pages = vm->nr_pages;
+	first_chunk->hdr.flags = flags;
+	first_chunk->hdr.order = order;
+
+	for (int i = 0; i < vm->nr_pages; i += (1 << order)) {
+		phys_addr_t phys = page_to_phys(vm->pages[i]);
+
+		err = __kho_preserve_order(track, PHYS_PFN(phys), order);
+		if (err)
+			goto err_free;
+
+		chunk->phys[chunk->hdr.num_elms] = phys;
+		chunk->hdr.num_elms++;
+		if (chunk->hdr.num_elms == ARRAY_SIZE(chunk->phys)) {
+			chunk = new_vmalloc_chunk(chunk);
+			if (!chunk)
+				goto err_free;
+		}
+	}
+
+	*preservation = virt_to_phys(first_chunk);
+	return 0;
+
+err_free:
+	kho_vmalloc_free_chunks(first_chunk);
+	return err;
+}
+EXPORT_SYMBOL_GPL(kho_preserve_vmalloc);
+
+/**
+ * kho_restore_vmalloc - recreates and populates an area in vmalloc address
+ * space from the preserved memory.
+ * @preservation: physical address of the preservation metadata.
+ *
+ * Recreates an area in vmalloc address space and populates it with memory that
+ * was preserved using kho_preserve_vmalloc().
+ *
+ * Return: pointer to the area in the vmalloc address space, NULL on failure.
+ */
+void *kho_restore_vmalloc(phys_addr_t preservation)
+{
+	struct kho_vmalloc_chunk *chunk = phys_to_virt(preservation);
+	unsigned int align, order, shift, flags;
+	unsigned int idx = 0, nr;
+	unsigned long addr, size;
+	struct vm_struct *area;
+	struct page **pages;
+	int err;
+
+	flags = chunk->hdr.flags;
+	if (flags & ~KHO_VMALLOC_FLAGS_MASK)
+		return NULL;
+
+	nr = chunk->hdr.total_pages;
+	pages = kvmalloc_array(nr, sizeof(*pages), GFP_KERNEL);
+	if (!pages)
+		return NULL;
+	order = chunk->hdr.order;
+	shift = PAGE_SHIFT + order;
+	align = 1 << shift;
+
+	while (chunk) {
+		struct page *page;
+
+		for (int i = 0; i < chunk->hdr.num_elms; i++) {
+			phys_addr_t phys = chunk->phys[i];
+
+			for (int j = 0; j < (1 << order); j++) {
+				page = phys_to_page(phys);
+				kho_restore_page(page, 0);
+				pages[idx++] = page;
+				phys += PAGE_SIZE;
+			}
+		}
+
+		page = virt_to_page(chunk);
+		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
+		kho_restore_page(page, 0);
+		__free_page(page);
+	}
+
+	area = __get_vm_area_node(nr * PAGE_SIZE, align, shift, flags,
+				  VMALLOC_START, VMALLOC_END, NUMA_NO_NODE,
+				  GFP_KERNEL, __builtin_return_address(0));
+	if (!area)
+		goto err_free_pages_array;
+
+	addr = (unsigned long)area->addr;
+	size = get_vm_area_size(area);
+	err = vmap_pages_range(addr, addr + size, PAGE_KERNEL, pages, shift);
+	if (err)
+		goto err_free_vm_area;
+
+	return area->addr;
+
+err_free_vm_area:
+	free_vm_area(area);
+err_free_pages_array:
+	kvfree(pages);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
+
 /* Handling for debug/kho/out */
 
 static struct dentry *debugfs_root;
-- 
2.50.1

On Mon, Sep 08 2025, Mike Rapoport wrote:

> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
> A vmalloc allocation is preserved using binary structure similar to
> global KHO memory tracker. It's a linked list of pages where each page
> is an array of physical address of pages in vmalloc area.
>
> kho_preserve_vmalloc() hands out the physical address of the head page
> to the caller. This address is used as the argument to
> kho_vmalloc_restore() to restore the mapping in the vmalloc address
> space and populate it with the preserved pages.
>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>  include/linux/kexec_handover.h |  12 ++
>  kernel/kexec_handover.c        | 200 +++++++++++++++++++++++++++++++++
>  2 files changed, 212 insertions(+)
>
> diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> index 348844cffb13..b7bf3bf11019 100644
> --- a/include/linux/kexec_handover.h
> +++ b/include/linux/kexec_handover.h
> @@ -42,8 +42,10 @@ struct kho_serialization;
>  bool kho_is_enabled(void);
>  
>  int kho_preserve_folio(struct folio *folio);
> +int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation);
>  int kho_preserve_phys(phys_addr_t phys, size_t size);
>  struct folio *kho_restore_folio(phys_addr_t phys);
> +void *kho_restore_vmalloc(phys_addr_t preservation);
>  int kho_add_subtree(struct kho_serialization *ser, const char *name, void *fdt);
>  int kho_retrieve_subtree(const char *name, phys_addr_t *phys);
>  
> @@ -70,11 +72,21 @@ static inline int kho_preserve_phys(phys_addr_t phys, size_t size)
>  	return -EOPNOTSUPP;
>  }
>  
> +static inline int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  static inline struct folio *kho_restore_folio(phys_addr_t phys)
>  {
>  	return NULL;
>  }
>  
> +static inline void *kho_restore_vmalloc(phys_addr_t preservation)
> +{
> +	return NULL;
> +}
> +
>  static inline int kho_add_subtree(struct kho_serialization *ser,
>  				  const char *name, void *fdt)
>  {
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index 8079fc4b9189..1177cc5ffa1a 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/vmalloc.h>
>  
>  #include <asm/early_ioremap.h>
>  
> @@ -742,6 +743,205 @@ int kho_preserve_phys(phys_addr_t phys, size_t size)
>  }
>  EXPORT_SYMBOL_GPL(kho_preserve_phys);
>  
> +struct kho_vmalloc_chunk;
> +
> +struct kho_vmalloc_hdr {
> +	DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *);
> +	unsigned int total_pages;	/* only valid in the first chunk */
> +	unsigned int flags;		/* only valid in the first chunk */
> +	unsigned short order;		/* only valid in the first chunk */
> +	unsigned short num_elms;

I think it the serialization format would be cleaner if these were
defined in a separate structure that holds the metadata instead of being
defined in each page and then ignored in most of them.

If the caller can save 8 bytes (phys addr of first page), it might as
well save 16 instead. Something like the below perhaps?

struct kho_vmalloc {
	DECLARE_KHOSER_PTR(first, struct kho_vmalloc_chunk *);
	unsigned int total_pages;
	unsigned short flags;
	unsigned short order;
};

And then kho_vmalloc_hdr becomes simply:

struct kho_vmalloc_hdr {
	DECLARE_KHOSER_PTR(next, struct kho_vmalloc_chunk *);
};

You don't even need num_elms since you have the list be zero-terminated.

> +};
> +
> +#define KHO_VMALLOC_SIZE				\
> +	((PAGE_SIZE - sizeof(struct kho_vmalloc_hdr)) / \
> +	 sizeof(phys_addr_t))
> +
> +struct kho_vmalloc_chunk {
> +	struct kho_vmalloc_hdr hdr;
> +	phys_addr_t phys[KHO_VMALLOC_SIZE];
> +};
> +
> +static_assert(sizeof(struct kho_vmalloc_chunk) == PAGE_SIZE);
> +
> +#define KHO_VMALLOC_FLAGS_MASK	(VM_ALLOC | VM_ALLOW_HUGE_VMAP)

I don't think it is a good idea to re-use VM flags. This can make adding
more flags later down the line ugly. I think it would be better to
define KHO_VMALLOC_FL* instead.

> +
> +static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)
> +{
> +	struct kho_vmalloc_chunk *chunk;
> +	int err;
> +
> +	chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (!chunk)
> +		return NULL;
> +
> +	err = kho_preserve_phys(virt_to_phys(chunk), PAGE_SIZE);
> +	if (err)
> +		goto err_free;
> +	if (cur)
> +		KHOSER_STORE_PTR(cur->hdr.next, chunk);
> +	return chunk;
> +
> +err_free:
> +	kfree(chunk);
> +	return NULL;
> +}
> +
> +static void kho_vmalloc_free_chunks(struct kho_vmalloc_chunk *first_chunk)
> +{
> +	struct kho_mem_track *track = &kho_out.ser.track;
> +	struct kho_vmalloc_chunk *chunk = first_chunk;
> +
> +	while (chunk) {
> +		unsigned long pfn = PHYS_PFN(virt_to_phys(chunk));
> +		struct kho_vmalloc_chunk *tmp = chunk;
> +
> +		__kho_unpreserve(track, pfn, pfn + 1);

This doesn't unpreserve the pages contained in the chunk, which
kho_preserve_vmalloc() preserved.

> +
> +		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
> +		kfree(tmp);
> +	}
> +}
> +
> +/**
> + * kho_preserve_vmalloc - preserve memory allocated with vmalloc() across kexec
> + * @ptr: pointer to the area in vmalloc address space
> + * @preservation: returned physical address of preservation metadata
> + *
> + * Instructs KHO to preserve the area in vmalloc address space at @ptr. The
> + * physical pages mapped at @ptr will be preserved and on successful return
> + * @preservation will hold the physical address of a structure that describes
> + * the preservation.
> + *
> + * NOTE: The memory allocated with vmalloc_node() variants cannot be reliably
> + * restored on the same node
> + *
> + * Return: 0 on success, error code on failure
> + */
> +int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation)
> +{
> +	struct kho_mem_track *track = &kho_out.ser.track;
> +	struct kho_vmalloc_chunk *chunk, *first_chunk;
> +	struct vm_struct *vm = find_vm_area(ptr);
> +	unsigned int order, flags;
> +	int err;
> +
> +	if (!vm)
> +		return -EINVAL;
> +
> +	if (vm->flags & ~KHO_VMALLOC_FLAGS_MASK)
> +		return -EOPNOTSUPP;
> +
> +	flags = vm->flags & KHO_VMALLOC_FLAGS_MASK;
> +	order = get_vm_area_page_order(vm);
> +
> +	chunk = new_vmalloc_chunk(NULL);
> +	if (!chunk)
> +		return -ENOMEM;
> +	first_chunk = chunk;
> +	first_chunk->hdr.total_pages = vm->nr_pages;
> +	first_chunk->hdr.flags = flags;
> +	first_chunk->hdr.order = order;
> +
> +	for (int i = 0; i < vm->nr_pages; i += (1 << order)) {
> +		phys_addr_t phys = page_to_phys(vm->pages[i]);
> +
> +		err = __kho_preserve_order(track, PHYS_PFN(phys), order);
> +		if (err)
> +			goto err_free;
> +
> +		chunk->phys[chunk->hdr.num_elms] = phys;
> +		chunk->hdr.num_elms++;
> +		if (chunk->hdr.num_elms == ARRAY_SIZE(chunk->phys)) {
> +			chunk = new_vmalloc_chunk(chunk);
> +			if (!chunk)
> +				goto err_free;
> +		}
> +	}
> +
> +	*preservation = virt_to_phys(first_chunk);
> +	return 0;
> +
> +err_free:
> +	kho_vmalloc_free_chunks(first_chunk);
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(kho_preserve_vmalloc);
> +
> +/**
> + * kho_restore_vmalloc - recreates and populates an area in vmalloc address
> + * space from the preserved memory.
> + * @preservation: physical address of the preservation metadata.
> + *
> + * Recreates an area in vmalloc address space and populates it with memory that
> + * was preserved using kho_preserve_vmalloc().
> + *
> + * Return: pointer to the area in the vmalloc address space, NULL on failure.
> + */
> +void *kho_restore_vmalloc(phys_addr_t preservation)
> +{
> +	struct kho_vmalloc_chunk *chunk = phys_to_virt(preservation);
> +	unsigned int align, order, shift, flags;
> +	unsigned int idx = 0, nr;
> +	unsigned long addr, size;
> +	struct vm_struct *area;
> +	struct page **pages;
> +	int err;
> +
> +	flags = chunk->hdr.flags;
> +	if (flags & ~KHO_VMALLOC_FLAGS_MASK)
> +		return NULL;
> +
> +	nr = chunk->hdr.total_pages;
> +	pages = kvmalloc_array(nr, sizeof(*pages), GFP_KERNEL);
> +	if (!pages)
> +		return NULL;
> +	order = chunk->hdr.order;
> +	shift = PAGE_SHIFT + order;
> +	align = 1 << shift;
> +
> +	while (chunk) {
> +		struct page *page;
> +
> +		for (int i = 0; i < chunk->hdr.num_elms; i++) {
> +			phys_addr_t phys = chunk->phys[i];
> +
> +			for (int j = 0; j < (1 << order); j++) {
> +				page = phys_to_page(phys);
> +				kho_restore_page(page, 0);
> +				pages[idx++] = page;

This can buffer-overflow if the previous kernel was buggy and added too
many pages. Perhaps keep check for this?

> +				phys += PAGE_SIZE;
> +			}
> +		}
> +
> +		page = virt_to_page(chunk);
> +		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
> +		kho_restore_page(page, 0);
> +		__free_page(page);
> +	}
> +
> +	area = __get_vm_area_node(nr * PAGE_SIZE, align, shift, flags,
> +				  VMALLOC_START, VMALLOC_END, NUMA_NO_NODE,
> +				  GFP_KERNEL, __builtin_return_address(0));
> +	if (!area)
> +		goto err_free_pages_array;
> +
> +	addr = (unsigned long)area->addr;
> +	size = get_vm_area_size(area);
> +	err = vmap_pages_range(addr, addr + size, PAGE_KERNEL, pages, shift);
> +	if (err)
> +		goto err_free_vm_area;
> +
> +	return area->addr;

You should free the pages array before returning here.

> +
> +err_free_vm_area:
> +	free_vm_area(area);
> +err_free_pages_array:
> +	kvfree(pages);
> +	return NULL;
> +}
> +EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
> +
>  /* Handling for debug/kho/out */
>  
>  static struct dentry *debugfs_root;

-- 
Regards,
Pratyush Yadav

Hi Mike,

Couple more thoughts.

On Mon, Sep 08 2025, Pratyush Yadav wrote:

> On Mon, Sep 08 2025, Mike Rapoport wrote:
>
>> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>>
>> A vmalloc allocation is preserved using binary structure similar to
>> global KHO memory tracker. It's a linked list of pages where each page
>> is an array of physical address of pages in vmalloc area.
>>
>> kho_preserve_vmalloc() hands out the physical address of the head page
>> to the caller. This address is used as the argument to
>> kho_vmalloc_restore() to restore the mapping in the vmalloc address
>> space and populate it with the preserved pages.
>>
>> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
[...]
>> +/**
>> + * kho_restore_vmalloc - recreates and populates an area in vmalloc address
>> + * space from the preserved memory.
>> + * @preservation: physical address of the preservation metadata.
>> + *
>> + * Recreates an area in vmalloc address space and populates it with memory that
>> + * was preserved using kho_preserve_vmalloc().
>> + *
>> + * Return: pointer to the area in the vmalloc address space, NULL on failure.
>> + */
>> +void *kho_restore_vmalloc(phys_addr_t preservation)
>> +{
>> +	struct kho_vmalloc_chunk *chunk = phys_to_virt(preservation);
>> +	unsigned int align, order, shift, flags;
>> +	unsigned int idx = 0, nr;
>> +	unsigned long addr, size;
>> +	struct vm_struct *area;
>> +	struct page **pages;
>> +	int err;
>> +
>> +	flags = chunk->hdr.flags;
>> +	if (flags & ~KHO_VMALLOC_FLAGS_MASK)
>> +		return NULL;
>> +
>> +	nr = chunk->hdr.total_pages;
>> +	pages = kvmalloc_array(nr, sizeof(*pages), GFP_KERNEL);
>> +	if (!pages)
>> +		return NULL;
>> +	order = chunk->hdr.order;
>> +	shift = PAGE_SHIFT + order;
>> +	align = 1 << shift;
>> +
>> +	while (chunk) {
>> +		struct page *page;
>> +
>> +		for (int i = 0; i < chunk->hdr.num_elms; i++) {
>> +			phys_addr_t phys = chunk->phys[i];
>> +
>> +			for (int j = 0; j < (1 << order); j++) {
>> +				page = phys_to_page(phys);
>> +				kho_restore_page(page, 0);
>> +				pages[idx++] = page;
>
> This can buffer-overflow if the previous kernel was buggy and added too
> many pages. Perhaps keep check for this?

Thinking about this a bit more, I think this should check that we found
_exactly_ chunk->hdr.total_pages pages, and should error out otherwise.
If too few are found, pages array will contain bogus data, if too many,
buffer overflow.

Also, I am not a fan of using kho_restore_page() directly. I think the
vmalloc preservation is a layer above core KHO, and it should use the
public KHO APIs. It really doesn't need to poke into internal APIs. If
any of the public APIs are insufficient, we should add new ones.

I don't suppose I'd insist on it, but something to consider since you
are likely going to do another revision anyway.

>
>> +				phys += PAGE_SIZE;
>> +			}
>> +		}
>> +
>> +		page = virt_to_page(chunk);
>> +		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
>> +		kho_restore_page(page, 0);
>> +		__free_page(page);
>> +	}
>> +
>> +	area = __get_vm_area_node(nr * PAGE_SIZE, align, shift, flags,
>> +				  VMALLOC_START, VMALLOC_END, NUMA_NO_NODE,
>> +				  GFP_KERNEL, __builtin_return_address(0));
>> +	if (!area)
>> +		goto err_free_pages_array;
>> +
>> +	addr = (unsigned long)area->addr;
>> +	size = get_vm_area_size(area);
>> +	err = vmap_pages_range(addr, addr + size, PAGE_KERNEL, pages, shift);
>> +	if (err)
>> +		goto err_free_vm_area;
>> +
>> +	return area->addr;
>
> You should free the pages array before returning here.
>
>> +
>> +err_free_vm_area:
>> +	free_vm_area(area);
>> +err_free_pages_array:
>> +	kvfree(pages);
>> +	return NULL;
>> +}
>> +EXPORT_SYMBOL_GPL(kho_restore_vmalloc);
>> +
>>  /* Handling for debug/kho/out */
>>  
>>  static struct dentry *debugfs_root;

-- 
Regards,
Pratyush Yadav

On Mon, Sep 08, 2025 at 08:12:59PM +0200, Pratyush Yadav wrote:
> > +#define KHO_VMALLOC_FLAGS_MASK	(VM_ALLOC | VM_ALLOW_HUGE_VMAP)
> 
> I don't think it is a good idea to re-use VM flags. This can make adding
> more flags later down the line ugly. I think it would be better to
> define KHO_VMALLOC_FL* instead.

+1

This kind of stuff should be avoided, it becomes a very sneaky ABI.

Jason

On Mon, Sep 08, 2025 at 01:35:27PM +0300, Mike Rapoport wrote:
> +static struct kho_vmalloc_chunk *new_vmalloc_chunk(struct kho_vmalloc_chunk *cur)
> +{
> +	struct kho_vmalloc_chunk *chunk;
> +	int err;
> +
> +	chunk = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (!chunk)
> +		return NULL;
> +
> +	err = kho_preserve_phys(virt_to_phys(chunk), PAGE_SIZE);
> +	if (err)
> +		goto err_free;

kzalloc() cannot be preserved, the only thing we support today is
alloc_page(), so this code pattern shouldn't exist.

Call alloc_page() and use a kho_preserve_page/folio() like the luo
patches were doing. The pattern seems common it probably needs a small
alloc/free helper.

> +	for (int i = 0; i < vm->nr_pages; i += (1 << order)) {
> +		phys_addr_t phys = page_to_phys(vm->pages[i]);
> +
> +		err = __kho_preserve_order(track, PHYS_PFN(phys), order);
> +		if (err)
> +			goto err_free;

I think you should make a helper inline to document what is happening here:

/*
 * Preserve a contiguous aligned list of order 0 pages that aggregate
 * to a higher order allocation. Must be restored using
 * kho_restore_page() on each order 0 page.
 */
kho_preserve_pages(page, order);

Jason