[PATCH v2] kasan: speed up mte_set_mem_tag_range

[Evgenii Stepanov]

Use DC GVA / DC GZVA to speed up KASan memory tagging in HW tags mode.

The first cacheline is always tagged using STG/STZG even if the address is
cacheline-aligned, as benchmarks show it is faster than a conditional
branch.

Signed-off-by: Evgenii Stepanov <eugenis at google.com>
Co-developed-by: Peter Collingbourne <pcc at google.com>
---
Changelog since v1:
- Added Co-developed-by.

 arch/arm64/include/asm/mte-kasan.h | 40 +------------------
 arch/arm64/lib/Makefile            |  2 +
 arch/arm64/lib/mte-kasan.S         | 63 ++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+), 39 deletions(-)
 create mode 100644 arch/arm64/lib/mte-kasan.S

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index ddd4d17cf9a0..e29a0e2ab35c 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -48,45 +48,7 @@ static inline u8 mte_get_random_tag(void)
 	return mte_get_ptr_tag(addr);
 }
 
-/*
- * Assign allocation tags for a region of memory based on the pointer tag.
- * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
- * size must be non-zero and MTE_GRANULE_SIZE aligned.
- */
-static inline void mte_set_mem_tag_range(void *addr, size_t size,
-						u8 tag, bool init)
-{
-	u64 curr, end;
-
-	if (!size)
-		return;
-
-	curr = (u64)__tag_set(addr, tag);
-	end = curr + size;
-
-	/*
-	 * 'asm volatile' is required to prevent the compiler to move
-	 * the statement outside of the loop.
-	 */
-	if (init) {
-		do {
-			asm volatile(__MTE_PREAMBLE "stzg %0, [%0]"
-				     :
-				     : "r" (curr)
-				     : "memory");
-			curr += MTE_GRANULE_SIZE;
-		} while (curr != end);
-	} else {
-		do {
-			asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
-				     :
-				     : "r" (curr)
-				     : "memory");
-			curr += MTE_GRANULE_SIZE;
-		} while (curr != end);
-	}
-}
-
+void mte_set_mem_tag_range(void *addr, size_t size, u8 tag, bool init);
 void mte_enable_kernel_sync(void);
 void mte_enable_kernel_async(void);
 void mte_init_tags(u64 max_tag);
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index d31e1169d9b8..c06ada79a437 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -18,3 +18,5 @@ obj-$(CONFIG_CRC32) += crc32.o
 obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
 
 obj-$(CONFIG_ARM64_MTE) += mte.o
+
+obj-$(CONFIG_KASAN_HW_TAGS) += mte-kasan.o
diff --git a/arch/arm64/lib/mte-kasan.S b/arch/arm64/lib/mte-kasan.S
new file mode 100644
index 000000000000..9f6975e2af60
--- /dev/null
+++ b/arch/arm64/lib/mte-kasan.S
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Google Inc.
+ */
+#include <linux/const.h>
+#include <linux/linkage.h>
+
+#include <asm/mte-def.h>
+
+	.arch	armv8.5-a+memtag
+
+	.macro  __set_mem_tag_range, stg, gva, start, size, linesize, tmp1, tmp2, tmp3
+	add	\tmp3, \start, \size
+	cmp	\size, \linesize, lsl #1
+	b.lt	.Lsmtr3_\@
+
+	sub	\tmp1, \linesize, #1
+	bic	\tmp2, \tmp3, \tmp1
+	orr	\tmp1, \start, \tmp1
+
+.Lsmtr1_\@:
+	\stg	\start, [\start], #MTE_GRANULE_SIZE
+	cmp	\start, \tmp1
+	b.lt	.Lsmtr1_\@
+
+.Lsmtr2_\@:
+	dc	\gva, \start
+	add	\start, \start, \linesize
+	cmp	\start, \tmp2
+	b.lt	.Lsmtr2_\@
+
+.Lsmtr3_\@:
+	cmp	\start, \tmp3
+	b.ge	.Lsmtr4_\@
+	\stg	\start, [\start], #MTE_GRANULE_SIZE
+	b	.Lsmtr3_\@
+.Lsmtr4_\@:
+	.endm
+
+/*
+ * Assign allocation tags for a region of memory based on the pointer tag.
+ * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
+ * size must be non-zero and MTE_GRANULE_SIZE aligned.
+ *   x0 - start address
+ *   x1 - region size
+ *   x2 - tag
+ *   x3 - bool init
+ */
+SYM_FUNC_START(mte_set_mem_tag_range)
+	mrs	x4, dczid_el0
+	and	w4, w4, #0xf
+	mov	x5, #4
+	lsl	x4, x5, x4
+
+	bfi	x0, x2, #56, #8
+
+	cbz	x3, .Lnoinit
+	__set_mem_tag_range stzg, gzva, x0, x1, x4, x2, x3, x5
+	ret
+.Lnoinit:
+	__set_mem_tag_range stg, gva, x0, x1, x4, x2, x3, x5
+	ret
+SYM_FUNC_END(mte_set_mem_tag_range)
-- 
2.31.1.751.gd2f1c929bd-goog