[PATCH v10 6/6] arm64: introduce copy_mc_to_kernel() implementation

From: Tong Tiangen
Date: Mon Jan 29 2024 - 08:48:15 EST

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The copy_mc_to_kernel() helper is memory copy implementation that handles
source exceptions. It can be used in memory copy scenarios that tolerate
hardware memory errors(e.g: pmem_read/dax_copy_to_iter).

Currnently, only x86 and ppc suuport this helper, after arm64 support
machine check safe framework, we introduce copy_mc_to_kernel()
implementation.

Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
---
arch/arm64/include/asm/string.h | 5 +
arch/arm64/include/asm/uaccess.h | 21 +++
arch/arm64/lib/Makefile | 2 +-
arch/arm64/lib/memcpy_mc.S | 257 +++++++++++++++++++++++++++++++
mm/kasan/shadow.c | 12 ++
5 files changed, 296 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/lib/memcpy_mc.S

diff --git a/arch/arm64/include/asm/string.h b/arch/arm64/include/asm/string.h
index 3a3264ff47b9..995b63c26e99 100644
--- a/arch/arm64/include/asm/string.h
+++ b/arch/arm64/include/asm/string.h
@@ -35,6 +35,10 @@ extern void *memchr(const void *, int, __kernel_size_t);
extern void *memcpy(void *, const void *, __kernel_size_t);
extern void *__memcpy(void *, const void *, __kernel_size_t);

+#define __HAVE_ARCH_MEMCPY_MC
+extern int memcpy_mcs(void *, const void *, __kernel_size_t);
+extern int __memcpy_mcs(void *, const void *, __kernel_size_t);
+
#define __HAVE_ARCH_MEMMOVE
extern void *memmove(void *, const void *, __kernel_size_t);
extern void *__memmove(void *, const void *, __kernel_size_t);
@@ -57,6 +61,7 @@ void memcpy_flushcache(void *dst, const void *src, size_t cnt);
*/

#define memcpy(dst, src, len) __memcpy(dst, src, len)
+#define memcpy_mcs(dst, src, len) __memcpy_mcs(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 14be5000c5a0..61e28ef2112a 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -425,4 +425,25 @@ static inline size_t probe_subpage_writeable(const char __user *uaddr,

#endif /* CONFIG_ARCH_HAS_SUBPAGE_FAULTS */

+#ifdef CONFIG_ARCH_HAS_COPY_MC
+/**
+ * copy_mc_to_kernel - memory copy that handles source exceptions
+ *
+ * @dst: destination address
+ * @src: source address
+ * @len: number of bytes to copy
+ *
+ * Return 0 for success, or #size if there was an exception.
+ */
+static inline unsigned long __must_check
+copy_mc_to_kernel(void *to, const void *from, unsigned long size)
+{
+ int ret;
+
+ ret = memcpy_mcs(to, from, size);
+ return (ret == -EFAULT) ? size : 0;
+}
+#define copy_mc_to_kernel copy_mc_to_kernel
+#endif
+
#endif /* __ASM_UACCESS_H */
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index a2fd865b816d..899d6ae9698c 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -3,7 +3,7 @@ lib-y := clear_user.o delay.o copy_from_user.o \
copy_to_user.o copy_page.o \
clear_page.o csum.o insn.o memchr.o memcpy.o \
memset.o memcmp.o strcmp.o strncmp.o strlen.o \
- strnlen.o strchr.o strrchr.o tishift.o
+ strnlen.o strchr.o strrchr.o tishift.o memcpy_mc.o

ifeq ($(CONFIG_KERNEL_MODE_NEON), y)
obj-$(CONFIG_XOR_BLOCKS) += xor-neon.o
diff --git a/arch/arm64/lib/memcpy_mc.S b/arch/arm64/lib/memcpy_mc.S
new file mode 100644
index 000000000000..7076b500d154
--- /dev/null
+++ b/arch/arm64/lib/memcpy_mc.S
@@ -0,0 +1,257 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2012-2021, Arm Limited.
+ *
+ * Adapted from the original at:
+ * https://github.com/ARM-software/optimized-routines/blob/afd6244a1f8d9229/string/aarch64/memcpy.S
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64, unaligned accesses.
+ *
+ */
+
+#define L(label) .L ## label
+
+#define dstin x0
+#define src x1
+#define count x2
+#define dst x3
+#define srcend x4
+#define dstend x5
+#define A_l x6
+#define A_lw w6
+#define A_h x7
+#define B_l x8
+#define B_lw w8
+#define B_h x9
+#define C_l x10
+#define C_lw w10
+#define C_h x11
+#define D_l x12
+#define D_h x13
+#define E_l x14
+#define E_h x15
+#define F_l x16
+#define F_h x17
+#define G_l count
+#define G_h dst
+#define H_l src
+#define H_h srcend
+#define tmp1 x14
+
+/* This implementation handles overlaps and supports both memcpy and memmove
+ from a single entry point. It uses unaligned accesses and branchless
+ sequences to keep the code small, simple and improve performance.
+
+ Copies are split into 3 main cases: small copies of up to 32 bytes, medium
+ copies of up to 128 bytes, and large copies. The overhead of the overlap
+ check is negligible since it is only required for large copies.
+
+ Large copies use a software pipelined loop processing 64 bytes per iteration.
+ The destination pointer is 16-byte aligned to minimize unaligned accesses.
+ The loop tail is handled by always copying 64 bytes from the end.
+*/
+
+SYM_FUNC_START(__pi_memcpy_mcs)
+ add srcend, src, count
+ add dstend, dstin, count
+ cmp count, 128
+ b.hi L(copy_long)
+ cmp count, 32
+ b.hi L(copy32_128)
+
+ /* Small copies: 0..32 bytes. */
+ cmp count, 16
+ b.lo L(copy16)
+ CPY_MC(9998f, ldp A_l, A_h, [src])
+ CPY_MC(9998f, ldp D_l, D_h, [srcend, -16])
+ CPY_MC(9998f, stp A_l, A_h, [dstin])
+ CPY_MC(9998f, stp D_l, D_h, [dstend, -16])
+ mov x0, #0
+ ret
+
+ /* Copy 8-15 bytes. */
+L(copy16):
+ tbz count, 3, L(copy8)
+ CPY_MC(9998f, ldr A_l, [src])
+ CPY_MC(9998f, ldr A_h, [srcend, -8])
+ CPY_MC(9998f, str A_l, [dstin])
+ CPY_MC(9998f, str A_h, [dstend, -8])
+ mov x0, #0
+ ret
+
+ .p2align 3
+ /* Copy 4-7 bytes. */
+L(copy8):
+ tbz count, 2, L(copy4)
+ CPY_MC(9998f, ldr A_lw, [src])
+ CPY_MC(9998f, ldr B_lw, [srcend, -4])
+ CPY_MC(9998f, str A_lw, [dstin])
+ CPY_MC(9998f, str B_lw, [dstend, -4])
+ mov x0, #0
+ ret
+
+ /* Copy 0..3 bytes using a branchless sequence. */
+L(copy4):
+ cbz count, L(copy0)
+ lsr tmp1, count, 1
+ CPY_MC(9998f, ldrb A_lw, [src])
+ CPY_MC(9998f, ldrb C_lw, [srcend, -1])
+ CPY_MC(9998f, ldrb B_lw, [src, tmp1])
+ CPY_MC(9998f, strb A_lw, [dstin])
+ CPY_MC(9998f, strb B_lw, [dstin, tmp1])
+ CPY_MC(9998f, strb C_lw, [dstend, -1])
+L(copy0):
+ mov x0, #0
+ ret
+
+ .p2align 4
+ /* Medium copies: 33..128 bytes. */
+L(copy32_128):
+ CPY_MC(9998f, ldp A_l, A_h, [src])
+ CPY_MC(9998f, ldp B_l, B_h, [src, 16])
+ CPY_MC(9998f, ldp C_l, C_h, [srcend, -32])
+ CPY_MC(9998f, ldp D_l, D_h, [srcend, -16])
+ cmp count, 64
+ b.hi L(copy128)
+ CPY_MC(9998f, stp A_l, A_h, [dstin])
+ CPY_MC(9998f, stp B_l, B_h, [dstin, 16])
+ CPY_MC(9998f, stp C_l, C_h, [dstend, -32])
+ CPY_MC(9998f, stp D_l, D_h, [dstend, -16])
+ mov x0, #0
+ ret
+
+ .p2align 4
+ /* Copy 65..128 bytes. */
+L(copy128):
+ CPY_MC(9998f, ldp E_l, E_h, [src, 32])
+ CPY_MC(9998f, ldp F_l, F_h, [src, 48])
+ cmp count, 96
+ b.ls L(copy96)
+ CPY_MC(9998f, ldp G_l, G_h, [srcend, -64])
+ CPY_MC(9998f, ldp H_l, H_h, [srcend, -48])
+ CPY_MC(9998f, stp G_l, G_h, [dstend, -64])
+ CPY_MC(9998f, stp H_l, H_h, [dstend, -48])
+L(copy96):
+ CPY_MC(9998f, stp A_l, A_h, [dstin])
+ CPY_MC(9998f, stp B_l, B_h, [dstin, 16])
+ CPY_MC(9998f, stp E_l, E_h, [dstin, 32])
+ CPY_MC(9998f, stp F_l, F_h, [dstin, 48])
+ CPY_MC(9998f, stp C_l, C_h, [dstend, -32])
+ CPY_MC(9998f, stp D_l, D_h, [dstend, -16])
+ mov x0, #0
+ ret
+
+ .p2align 4
+ /* Copy more than 128 bytes. */
+L(copy_long):
+ /* Use backwards copy if there is an overlap. */
+ sub tmp1, dstin, src
+ cbz tmp1, L(copy0)
+ cmp tmp1, count
+ b.lo L(copy_long_backwards)
+
+ /* Copy 16 bytes and then align dst to 16-byte alignment. */
+
+ CPY_MC(9998f, ldp D_l, D_h, [src])
+ and tmp1, dstin, 15
+ bic dst, dstin, 15
+ sub src, src, tmp1
+ add count, count, tmp1 /* Count is now 16 too large. */
+ CPY_MC(9998f, ldp A_l, A_h, [src, 16])
+ CPY_MC(9998f, stp D_l, D_h, [dstin])
+ CPY_MC(9998f, ldp B_l, B_h, [src, 32])
+ CPY_MC(9998f, ldp C_l, C_h, [src, 48])
+ CPY_MC(9998f, ldp D_l, D_h, [src, 64]!)
+ subs count, count, 128 + 16 /* Test and readjust count. */
+ b.ls L(copy64_from_end)
+
+L(loop64):
+ CPY_MC(9998f, stp A_l, A_h, [dst, 16])
+ CPY_MC(9998f, ldp A_l, A_h, [src, 16])
+ CPY_MC(9998f, stp B_l, B_h, [dst, 32])
+ CPY_MC(9998f, ldp B_l, B_h, [src, 32])
+ CPY_MC(9998f, stp C_l, C_h, [dst, 48])
+ CPY_MC(9998f, ldp C_l, C_h, [src, 48])
+ CPY_MC(9998f, stp D_l, D_h, [dst, 64]!)
+ CPY_MC(9998f, ldp D_l, D_h, [src, 64]!)
+ subs count, count, 64
+ b.hi L(loop64)
+
+ /* Write the last iteration and copy 64 bytes from the end. */
+L(copy64_from_end):
+ CPY_MC(9998f, ldp E_l, E_h, [srcend, -64])
+ CPY_MC(9998f, stp A_l, A_h, [dst, 16])
+ CPY_MC(9998f, ldp A_l, A_h, [srcend, -48])
+ CPY_MC(9998f, stp B_l, B_h, [dst, 32])
+ CPY_MC(9998f, ldp B_l, B_h, [srcend, -32])
+ CPY_MC(9998f, stp C_l, C_h, [dst, 48])
+ CPY_MC(9998f, ldp C_l, C_h, [srcend, -16])
+ CPY_MC(9998f, stp D_l, D_h, [dst, 64])
+ CPY_MC(9998f, stp E_l, E_h, [dstend, -64])
+ CPY_MC(9998f, stp A_l, A_h, [dstend, -48])
+ CPY_MC(9998f, stp B_l, B_h, [dstend, -32])
+ CPY_MC(9998f, stp C_l, C_h, [dstend, -16])
+ mov x0, #0
+ ret
+
+ .p2align 4
+
+ /* Large backwards copy for overlapping copies.
+ Copy 16 bytes and then align dst to 16-byte alignment. */
+L(copy_long_backwards):
+ CPY_MC(9998f, ldp D_l, D_h, [srcend, -16])
+ and tmp1, dstend, 15
+ sub srcend, srcend, tmp1
+ sub count, count, tmp1
+ CPY_MC(9998f, ldp A_l, A_h, [srcend, -16])
+ CPY_MC(9998f, stp D_l, D_h, [dstend, -16])
+ CPY_MC(9998f, ldp B_l, B_h, [srcend, -32])
+ CPY_MC(9998f, ldp C_l, C_h, [srcend, -48])
+ CPY_MC(9998f, ldp D_l, D_h, [srcend, -64]!)
+ sub dstend, dstend, tmp1
+ subs count, count, 128
+ b.ls L(copy64_from_start)
+
+L(loop64_backwards):
+ CPY_MC(9998f, stp A_l, A_h, [dstend, -16])
+ CPY_MC(9998f, ldp A_l, A_h, [srcend, -16])
+ CPY_MC(9998f, stp B_l, B_h, [dstend, -32])
+ CPY_MC(9998f, ldp B_l, B_h, [srcend, -32])
+ CPY_MC(9998f, stp C_l, C_h, [dstend, -48])
+ CPY_MC(9998f, ldp C_l, C_h, [srcend, -48])
+ CPY_MC(9998f, stp D_l, D_h, [dstend, -64]!)
+ CPY_MC(9998f, ldp D_l, D_h, [srcend, -64]!)
+ subs count, count, 64
+ b.hi L(loop64_backwards)
+
+ /* Write the last iteration and copy 64 bytes from the start. */
+L(copy64_from_start):
+ CPY_MC(9998f, ldp G_l, G_h, [src, 48])
+ CPY_MC(9998f, stp A_l, A_h, [dstend, -16])
+ CPY_MC(9998f, ldp A_l, A_h, [src, 32])
+ CPY_MC(9998f, stp B_l, B_h, [dstend, -32])
+ CPY_MC(9998f, ldp B_l, B_h, [src, 16])
+ CPY_MC(9998f, stp C_l, C_h, [dstend, -48])
+ CPY_MC(9998f, ldp C_l, C_h, [src])
+ CPY_MC(9998f, stp D_l, D_h, [dstend, -64])
+ CPY_MC(9998f, stp G_l, G_h, [dstin, 48])
+ CPY_MC(9998f, stp A_l, A_h, [dstin, 32])
+ CPY_MC(9998f, stp B_l, B_h, [dstin, 16])
+ CPY_MC(9998f, stp C_l, C_h, [dstin])
+ mov x0, #0
+ ret
+
+9998: mov x0, #-EFAULT
+ ret
+SYM_FUNC_END(__pi_memcpy_mcs)
+
+SYM_FUNC_ALIAS(__memcpy_mcs, __pi_memcpy_mcs)
+EXPORT_SYMBOL(__memcpy_mcs)
+SYM_FUNC_ALIAS_WEAK(memcpy_mcs, __memcpy_mcs)
+EXPORT_SYMBOL(memcpy_mcs)
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index 9ef84f31833f..e6519fd329b2 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -79,6 +79,18 @@ void *memcpy(void *dest, const void *src, size_t len)
}
#endif

+#ifdef __HAVE_ARCH_MEMCPY_MC
+#undef memcpy_mcs
+int memcpy_mcs(void *dest, const void *src, size_t len)
+{
+ if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
+ !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
+ return (unsigned long)len;
+
+ return __memcpy_mcs(dest, src, len);
+}
+#endif
+
void *__asan_memset(void *addr, int c, ssize_t len)
{
if (!kasan_check_range(addr, len, true, _RET_IP_))
--
2.25.1

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Next in thread: Mark Rutland: "Re: [PATCH v10 6/6] arm64: introduce copy_mc_to_kernel() implementation"
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