[PATCH 3/5] arm64: mte: Define the number of bytes for storing the tags in a page

[Catalin Marinas]

Rather than explicitly calculating the number of bytes for a compact tag
storage format corresponding to a page, just add a MTE_PAGE_TAG_STORAGE
macro. With the current MTE implementation of 4 bits per tag, we store
2 tags in a byte.

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
---
 arch/arm64/include/asm/mte-def.h | 1 +
 arch/arm64/lib/mte.S             | 4 ++--
 arch/arm64/mm/mteswap.c          | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/mte-def.h b/arch/arm64/include/asm/mte-def.h
index 626d359b396e..14ee86b019c2 100644
--- a/arch/arm64/include/asm/mte-def.h
+++ b/arch/arm64/include/asm/mte-def.h
@@ -11,6 +11,7 @@
 #define MTE_TAG_SHIFT		56
 #define MTE_TAG_SIZE		4
 #define MTE_TAG_MASK		GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
+#define MTE_PAGE_TAG_STORAGE	(MTE_GRANULES_PER_PAGE * MTE_TAG_SIZE / 8)
 
 #define __MTE_PREAMBLE		ARM64_ASM_PREAMBLE ".arch_extension memtag\n"
 
diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
index e83643b3995f..62a1025aa118 100644
--- a/arch/arm64/lib/mte.S
+++ b/arch/arm64/lib/mte.S
@@ -128,7 +128,7 @@ SYM_FUNC_END(mte_copy_tags_to_user)
 /*
  * Save the tags in a page
  *   x0 - page address
- *   x1 - tag storage
+ *   x1 - tag storage, MTE_PAGE_TAG_STORAGE bytes
  */
 SYM_FUNC_START(mte_save_page_tags)
 	multitag_transfer_size x7, x5
@@ -152,7 +152,7 @@ SYM_FUNC_END(mte_save_page_tags)
 /*
  * Restore the tags in a page
  *   x0 - page address
- *   x1 - tag storage
+ *   x1 - tag storage, MTE_PAGE_TAG_STORAGE bytes
  */
 SYM_FUNC_START(mte_restore_page_tags)
 	multitag_transfer_size x7, x5
diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c
index 7c4ef56265ee..a9e50e930484 100644
--- a/arch/arm64/mm/mteswap.c
+++ b/arch/arm64/mm/mteswap.c
@@ -12,7 +12,7 @@ static DEFINE_XARRAY(mte_pages);
 void *mte_allocate_tag_storage(void)
 {
 	/* tags granule is 16 bytes, 2 tags stored per byte */
-	return kmalloc(PAGE_SIZE / 16 / 2, GFP_KERNEL);
+	return kmalloc(MTE_PAGE_TAG_STORAGE, GFP_KERNEL);
 }
 
 void mte_free_tag_storage(char *storage)