[PATCH 4/4] arm64: mte: Optimize mte_assign_mem_tag_range()

From: Vincenzo Frascino
Date: Wed Jan 06 2021 - 06:58:16 EST


mte_assign_mem_tag_range() is called on production KASAN HW hot
paths. It makes sense to optimize it in an attempt to reduce the
overhead.

Optimize mte_assign_mem_tag_range() based on the indications provided at
[1].

[1] https://lore.kernel.org/r/CAAeHK+wCO+J7D1_T89DG+jJrPLk3X9RsGFKxJGd0ZcUFjQT-9Q@xxxxxxxxxxxxxx/

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
---
arch/arm64/include/asm/mte.h | 26 +++++++++++++++++++++++++-
arch/arm64/lib/mte.S | 15 ---------------
2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index c757ff756e09..ac134a74e1a1 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -50,7 +50,31 @@ long get_mte_ctrl(struct task_struct *task);
int mte_ptrace_copy_tags(struct task_struct *child, long request,
unsigned long addr, unsigned long data);

-void mte_assign_mem_tag_range(void *addr, size_t size);
+static inline void mte_assign_mem_tag_range(void *addr, size_t size)
+{
+ u64 _addr = (u64)addr;
+ u64 _end = _addr + size;
+
+ /*
+ * This function must be invoked from an MTE enabled context.
+ *
+ * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
+ * size must be non-zero and MTE_GRANULE_SIZE aligned.
+ */
+ do {
+ /*
+ * 'asm volatile' is required to prevent the compiler to move
+ * the statement outside of the loop.
+ */
+ asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
+ :
+ : "r" (_addr)
+ : "memory");
+
+ _addr += MTE_GRANULE_SIZE;
+ } while (_addr < _end);
+}
+

#else /* CONFIG_ARM64_MTE */

diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
index 9e1a12e10053..a0a650451510 100644
--- a/arch/arm64/lib/mte.S
+++ b/arch/arm64/lib/mte.S
@@ -150,18 +150,3 @@ SYM_FUNC_START(mte_restore_page_tags)
ret
SYM_FUNC_END(mte_restore_page_tags)

-/*
- * Assign allocation tags for a region of memory based on the pointer tag
- * x0 - source pointer
- * x1 - size
- *
- * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
- * size must be non-zero and MTE_GRANULE_SIZE aligned.
- */
-SYM_FUNC_START(mte_assign_mem_tag_range)
-1: stg x0, [x0]
- add x0, x0, #MTE_GRANULE_SIZE
- subs x1, x1, #MTE_GRANULE_SIZE
- b.gt 1b
- ret
-SYM_FUNC_END(mte_assign_mem_tag_range)
--
2.29.2