[PATCH] xen/arm: guest_walk: Only generate necessary offsets/masks

Julien Grall posted 1 patch 1 week, 1 day ago
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git fetch https://gitlab.com/xen-project/patchew/xen tags/patchew/20210405162046.9353-1-julien@xen.org
xen/arch/arm/guest_walk.c  | 37 ++---------------
xen/include/asm-arm/lpae.h | 82 +++++++++++++-------------------------
2 files changed, 30 insertions(+), 89 deletions(-)

[PATCH] xen/arm: guest_walk: Only generate necessary offsets/masks

Posted by Julien Grall 1 week, 1 day ago
From: Julien Grall <jgrall@amazon.com>

At the moment, we are computing offsets/masks for each level and
granularity. This is a bit of waste given that we only need to
know the offsets/masks for the granularity used by the guest.

All the LPAE information can easily be inferred with just the
page shift for a given granularity and the level.

So rather than providing a set of helpers per granularity, we can
provide a single set that takes the granularity and the level in
parameters.

With the new helpers in place, we can rework guest_walk_ld() to
only compute necessary information.

Signed-off-by: Julien Grall <julien@amazon.com>
---
 xen/arch/arm/guest_walk.c  | 37 ++---------------
 xen/include/asm-arm/lpae.h | 82 +++++++++++++-------------------------
 2 files changed, 30 insertions(+), 89 deletions(-)

diff --git a/xen/arch/arm/guest_walk.c b/xen/arch/arm/guest_walk.c
index b4496c4c86c6..87de40d0cb68 100644
--- a/xen/arch/arm/guest_walk.c
+++ b/xen/arch/arm/guest_walk.c
@@ -372,38 +372,6 @@ static bool guest_walk_ld(const struct vcpu *v,
     register_t tcr = READ_SYSREG(TCR_EL1);
     struct domain *d = v->domain;
 
-#define OFFSETS(gva, gran)              \
-{                                       \
-    zeroeth_table_offset_##gran(gva),   \
-    first_table_offset_##gran(gva),     \
-    second_table_offset_##gran(gva),    \
-    third_table_offset_##gran(gva)      \
-}
-
-    const paddr_t offsets[3][4] = {
-        OFFSETS(gva, 4K),
-        OFFSETS(gva, 16K),
-        OFFSETS(gva, 64K)
-    };
-
-#undef OFFSETS
-
-#define MASKS(gran)                     \
-{                                       \
-    zeroeth_size(gran) - 1,             \
-    first_size(gran) - 1,               \
-    second_size(gran) - 1,              \
-    third_size(gran) - 1                \
-}
-
-    static const paddr_t masks[3][4] = {
-        MASKS(4K),
-        MASKS(16K),
-        MASKS(64K)
-    };
-
-#undef MASKS
-
     static const unsigned int grainsizes[3] = {
         PAGE_SHIFT_4K,
         PAGE_SHIFT_16K,
@@ -519,7 +487,7 @@ static bool guest_walk_ld(const struct vcpu *v,
          * Add offset given by the GVA to the translation table base address.
          * Shift the offset by 3 as it is 8-byte aligned.
          */
-        paddr |= offsets[gran][level] << 3;
+        paddr |= LPAE_TABLE_INDEX_GS(grainsizes[gran], level, gva) << 3;
 
         /* Access the guest's memory to read only one PTE. */
         ret = access_guest_memory_by_ipa(d, paddr, &pte, sizeof(lpae_t), false);
@@ -572,7 +540,8 @@ static bool guest_walk_ld(const struct vcpu *v,
 
     /* Make sure that the lower bits of the PTE's base address are zero. */
     mask = GENMASK_ULL(47, grainsizes[gran]);
-    *ipa = (pfn_to_paddr(pte.walk.base) & mask) | (gva & masks[gran][level]);
+    *ipa = (pfn_to_paddr(pte.walk.base) & mask) |
+        (gva & (LEVEL_SIZE_GS(grainsizes[gran], level) - 1));
 
     /*
      * Set permissions so that the caller can check the flags by herself. Note
diff --git a/xen/include/asm-arm/lpae.h b/xen/include/asm-arm/lpae.h
index 4797f9cee494..e94de2e7d8e8 100644
--- a/xen/include/asm-arm/lpae.h
+++ b/xen/include/asm-arm/lpae.h
@@ -160,63 +160,35 @@ static inline bool lpae_is_superpage(lpae_t pte, unsigned int level)
 #define lpae_set_mfn(pte, mfn)  ((pte).walk.base = mfn_x(mfn))
 
 /*
- * AArch64 supports pages with different sizes (4K, 16K, and 64K). To enable
- * page table walks for various configurations, the following helpers enable
- * walking the translation table with varying page size granularities.
+ * AArch64 supports pages with different sizes (4K, 16K, and 64K).
+ * Provide a set of generic helpers that will compute various
+ * information based on the page granularity.
+ *
+ * Note the parameter 'gs' is the page shift of the granularity used.
+ * Some macro will evaluate 'gs' twice rather than storing in a
+ * variable. This is to allow using the macros in assembly.
+ */
+
+/*
+ * Granularity | PAGE_SHIFT | LPAE_SHIFT
+ * -------------------------------------
+ * 4K          | 12         | 9
+ * 16K         | 14         | 11
+ * 64K         | 16         | 13
+ *
+ * This is equivalent to LPAE_SHIFT = PAGE_SHIFT - 3
  */
+#define LPAE_SHIFT_GS(gs)         ((gs) - 3)
+#define LPAE_ENTRIES_GS(gs)       (_AC(1, U) << LPAE_SHIFT_GS(gs))
+#define LPAE_ENTRIES_MASK_GS(gs)  (LPAE_ENTRIES_GS(gs) - 1)
+
+#define LEVEL_ORDER_GS(gs, lvl)   ((3 - (lvl)) * LPAE_SHIFT_GS(gs))
+#define LEVEL_SHIFT_GS(gs, lvl)   (LEVEL_ORDER_GS(gs, lvl) + (gs))
+#define LEVEL_SIZE_GS(gs, lvl)    (_AT(paddr_t, 1) << LEVEL_SHIFT_GS(gs, lvl))
 
-#define LPAE_SHIFT_4K           (9)
-#define LPAE_SHIFT_16K          (11)
-#define LPAE_SHIFT_64K          (13)
-
-#define lpae_entries(gran)      (_AC(1,U) << LPAE_SHIFT_##gran)
-#define lpae_entry_mask(gran)   (lpae_entries(gran) - 1)
-
-#define third_shift(gran)       (PAGE_SHIFT_##gran)
-#define third_size(gran)        ((paddr_t)1 << third_shift(gran))
-
-#define second_shift(gran)      (third_shift(gran) + LPAE_SHIFT_##gran)
-#define second_size(gran)       ((paddr_t)1 << second_shift(gran))
-
-#define first_shift(gran)       (second_shift(gran) + LPAE_SHIFT_##gran)
-#define first_size(gran)        ((paddr_t)1 << first_shift(gran))
-
-/* Note that there is no zeroeth lookup level with a 64K granule size. */
-#define zeroeth_shift(gran)     (first_shift(gran) + LPAE_SHIFT_##gran)
-#define zeroeth_size(gran)      ((paddr_t)1 << zeroeth_shift(gran))
-
-#define TABLE_OFFSET(offs, gran)      (offs & lpae_entry_mask(gran))
-#define TABLE_OFFSET_HELPERS(gran)                                          \
-static inline paddr_t third_table_offset_##gran##K(paddr_t va)              \
-{                                                                           \
-    return TABLE_OFFSET((va >> third_shift(gran##K)), gran##K);             \
-}                                                                           \
-                                                                            \
-static inline paddr_t second_table_offset_##gran##K(paddr_t va)             \
-{                                                                           \
-    return TABLE_OFFSET((va >> second_shift(gran##K)), gran##K);            \
-}                                                                           \
-                                                                            \
-static inline paddr_t first_table_offset_##gran##K(paddr_t va)              \
-{                                                                           \
-    return TABLE_OFFSET((va >> first_shift(gran##K)), gran##K);             \
-}                                                                           \
-                                                                            \
-static inline paddr_t zeroeth_table_offset_##gran##K(paddr_t va)            \
-{                                                                           \
-    /* Note that there is no zeroeth lookup level with 64K granule sizes. */\
-    if ( gran == 64 )                                                       \
-        return 0;                                                           \
-    else                                                                    \
-        return TABLE_OFFSET((va >> zeroeth_shift(gran##K)), gran##K);       \
-}                                                                           \
-
-TABLE_OFFSET_HELPERS(4);
-TABLE_OFFSET_HELPERS(16);
-TABLE_OFFSET_HELPERS(64);
-
-#undef TABLE_OFFSET
-#undef TABLE_OFFSET_HELPERS
+/* Offset in the table at level 'lvl' */
+#define LPAE_TABLE_INDEX_GS(gs, lvl, addr)   \
+    (((addr) >> LEVEL_SHIFT_GS(gs, lvl)) & LPAE_ENTRIES_MASK_GS(gs))
 
 /* Generate an array @var containing the offset for each level from @addr */
 #define DECLARE_OFFSETS(var, addr)          \
-- 
2.17.1