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Date: Thu, 03 May 2018 17:06:11 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: linux-nvdimm@...ts.01.org
Cc: x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Tony Luck <tony.luck@...el.com>,
Al Viro <viro@...iv.linux.org.uk>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...capital.net>,
Peter Zijlstra <peterz@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>, hch@....de,
linux-kernel@...r.kernel.org, tony.luck@...el.com,
linux-fsdevel@...r.kernel.org
Subject: [PATCH v3 1/9] x86, memcpy_mcsafe: remove loop unrolling
In preparation for teaching memcpy_mcsafe() to return 'bytes remaining'
rather than pass / fail, simplify the implementation to remove loop
unrolling. The unrolling complicates the fault handling for negligible
benefit given modern CPUs perform loop stream detection.
Cc: <x86@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
arch/x86/include/asm/string_64.h | 4 +--
arch/x86/lib/memcpy_64.S | 59 ++++++--------------------------------
2 files changed, 12 insertions(+), 51 deletions(-)
diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 533f74c300c2..4752f8984923 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -116,7 +116,7 @@ int strcmp(const char *cs, const char *ct);
#endif
#define __HAVE_ARCH_MEMCPY_MCSAFE 1
-__must_check int memcpy_mcsafe_unrolled(void *dst, const void *src, size_t cnt);
+__must_check int __memcpy_mcsafe(void *dst, const void *src, size_t cnt);
DECLARE_STATIC_KEY_FALSE(mcsafe_key);
/**
@@ -138,7 +138,7 @@ memcpy_mcsafe(void *dst, const void *src, size_t cnt)
{
#ifdef CONFIG_X86_MCE
if (static_branch_unlikely(&mcsafe_key))
- return memcpy_mcsafe_unrolled(dst, src, cnt);
+ return __memcpy_mcsafe(dst, src, cnt);
else
#endif
memcpy(dst, src, cnt);
diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index 9a53a06e5a3e..54c971892db5 100644
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -184,11 +184,11 @@ ENDPROC(memcpy_orig)
#ifndef CONFIG_UML
/*
- * memcpy_mcsafe_unrolled - memory copy with machine check exception handling
+ * __memcpy_mcsafe - memory copy with machine check exception handling
* Note that we only catch machine checks when reading the source addresses.
* Writes to target are posted and don't generate machine checks.
*/
-ENTRY(memcpy_mcsafe_unrolled)
+ENTRY(__memcpy_mcsafe)
cmpl $8, %edx
/* Less than 8 bytes? Go to byte copy loop */
jb .L_no_whole_words
@@ -213,49 +213,18 @@ ENTRY(memcpy_mcsafe_unrolled)
jnz .L_copy_leading_bytes
.L_8byte_aligned:
- /* Figure out how many whole cache lines (64-bytes) to copy */
- movl %edx, %ecx
- andl $63, %edx
- shrl $6, %ecx
- jz .L_no_whole_cache_lines
-
- /* Loop copying whole cache lines */
-.L_cache_w0: movq (%rsi), %r8
-.L_cache_w1: movq 1*8(%rsi), %r9
-.L_cache_w2: movq 2*8(%rsi), %r10
-.L_cache_w3: movq 3*8(%rsi), %r11
- movq %r8, (%rdi)
- movq %r9, 1*8(%rdi)
- movq %r10, 2*8(%rdi)
- movq %r11, 3*8(%rdi)
-.L_cache_w4: movq 4*8(%rsi), %r8
-.L_cache_w5: movq 5*8(%rsi), %r9
-.L_cache_w6: movq 6*8(%rsi), %r10
-.L_cache_w7: movq 7*8(%rsi), %r11
- movq %r8, 4*8(%rdi)
- movq %r9, 5*8(%rdi)
- movq %r10, 6*8(%rdi)
- movq %r11, 7*8(%rdi)
- leaq 64(%rsi), %rsi
- leaq 64(%rdi), %rdi
- decl %ecx
- jnz .L_cache_w0
-
- /* Are there any trailing 8-byte words? */
-.L_no_whole_cache_lines:
movl %edx, %ecx
andl $7, %edx
shrl $3, %ecx
jz .L_no_whole_words
- /* Copy trailing words */
-.L_copy_trailing_words:
+.L_copy_words:
movq (%rsi), %r8
- mov %r8, (%rdi)
- leaq 8(%rsi), %rsi
- leaq 8(%rdi), %rdi
+ movq %r8, (%rdi)
+ addq $8, %rsi
+ addq $8, %rdi
decl %ecx
- jnz .L_copy_trailing_words
+ jnz .L_copy_words
/* Any trailing bytes? */
.L_no_whole_words:
@@ -276,8 +245,8 @@ ENTRY(memcpy_mcsafe_unrolled)
.L_done_memcpy_trap:
xorq %rax, %rax
ret
-ENDPROC(memcpy_mcsafe_unrolled)
-EXPORT_SYMBOL_GPL(memcpy_mcsafe_unrolled)
+ENDPROC(__memcpy_mcsafe)
+EXPORT_SYMBOL_GPL(__memcpy_mcsafe)
.section .fixup, "ax"
/* Return -EFAULT for any failure */
@@ -288,14 +257,6 @@ EXPORT_SYMBOL_GPL(memcpy_mcsafe_unrolled)
.previous
_ASM_EXTABLE_FAULT(.L_copy_leading_bytes, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w0, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w1, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w2, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w3, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w4, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w5, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w6, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_cache_w7, .L_memcpy_mcsafe_fail)
- _ASM_EXTABLE_FAULT(.L_copy_trailing_words, .L_memcpy_mcsafe_fail)
+ _ASM_EXTABLE_FAULT(.L_copy_words, .L_memcpy_mcsafe_fail)
_ASM_EXTABLE_FAULT(.L_copy_trailing_bytes, .L_memcpy_mcsafe_fail)
#endif
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