linux-kernel - [PATCH v2 4/4] arm64: mte: Optimize mte_assign_mem_tag

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Date:   Thu,  7 Jan 2021 17:29:08 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v2 4/4] arm64: mte: Optimize mte_assign_mem_tag_range()

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@mail.gmail.com/

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
---
 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 a60d3718baae..c341ce6b9779 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)
-- 
2.30.0