[PATCHV3 3/3] x86, ras: Add mcsafe_memcpy() function to recover from machine checks
From: Tony Luck
Date: Wed Dec 16 2015 - 12:23:49 EST
Using __copy_user_nocache() as inspiration create a memory copy
routine for use by kernel code with annotations to allow for
recovery from machine checks.
Notes:
1) We align the source address rather than the destination. This
means we never have to deal with a memory read that spans two
cache lines ... so we can provide a precise indication of
where the error occurred without having to re-execute at
a byte-by-byte level to find the exact spot like the original
did.
2) We 'or' BIT(63) into the return because this is the first
in a series of machine check safe functions. Some will copy
from user addresses, so may need to indicate an invalid user
address instead of a machine check.
3) This code doesn't play any cache games. Future functions can
use non-temporal loads/stores to meet needs of different callers.
4) Provide helpful macros to decode the return value.
Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
arch/x86/include/asm/mcsafe_copy.h | 11 +++
arch/x86/kernel/x8664_ksyms_64.c | 5 ++
arch/x86/lib/Makefile | 1 +
arch/x86/lib/mcsafe_copy.S | 142 +++++++++++++++++++++++++++++++++++++
4 files changed, 159 insertions(+)
create mode 100644 arch/x86/include/asm/mcsafe_copy.h
create mode 100644 arch/x86/lib/mcsafe_copy.S
diff --git a/arch/x86/include/asm/mcsafe_copy.h b/arch/x86/include/asm/mcsafe_copy.h
new file mode 100644
index 000000000000..d4dbd5a667a3
--- /dev/null
+++ b/arch/x86/include/asm/mcsafe_copy.h
@@ -0,0 +1,11 @@
+#ifndef _ASM_X86_MCSAFE_COPY_H
+#define _ASM_X86_MCSAFE_COPY_H
+
+u64 mcsafe_memcpy(void *dst, const void *src, unsigned size);
+
+#define COPY_MCHECK_ERRBIT BIT(63)
+#define COPY_HAD_MCHECK(ret) ((ret) & COPY_MCHECK_ERRBIT)
+#define COPY_MCHECK_REMAIN(ret) ((ret) & ~COPY_MCHECK_ERRBIT)
+
+#endif /* _ASM_MCSAFE_COPY_H */
+
diff --git a/arch/x86/kernel/x8664_ksyms_64.c b/arch/x86/kernel/x8664_ksyms_64.c
index a0695be19864..afab8b25dbc0 100644
--- a/arch/x86/kernel/x8664_ksyms_64.c
+++ b/arch/x86/kernel/x8664_ksyms_64.c
@@ -37,6 +37,11 @@ EXPORT_SYMBOL(__copy_user_nocache);
EXPORT_SYMBOL(_copy_from_user);
EXPORT_SYMBOL(_copy_to_user);
+#ifdef CONFIG_MCE_KERNEL_RECOVERY
+#include <asm/mcsafe_copy.h>
+EXPORT_SYMBOL(mcsafe_memcpy);
+#endif
+
EXPORT_SYMBOL(copy_page);
EXPORT_SYMBOL(clear_page);
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index f2587888d987..82bb0bf46b6b 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -21,6 +21,7 @@ lib-y += usercopy_$(BITS).o usercopy.o getuser.o putuser.o
lib-y += memcpy_$(BITS).o
lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o
+lib-$(CONFIG_MCE_KERNEL_RECOVERY) += mcsafe_copy.o
obj-y += msr.o msr-reg.o msr-reg-export.o
diff --git a/arch/x86/lib/mcsafe_copy.S b/arch/x86/lib/mcsafe_copy.S
new file mode 100644
index 000000000000..059b3a9642eb
--- /dev/null
+++ b/arch/x86/lib/mcsafe_copy.S
@@ -0,0 +1,142 @@
+/*
+ * Copyright (C) 2015 Intel Corporation
+ * Author: Tony Luck
+ *
+ * This software may be redistributed and/or modified under the terms of
+ * the GNU General Public License ("GPL") version 2 only as published by the
+ * Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+
+/*
+ * mcsafe_memcpy - 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(mcsafe_memcpy)
+ cmpl $8,%edx
+ jb 20f /* less then 8 bytes, go to byte copy loop */
+
+ /* check for bad alignment of source */
+ movl %esi,%ecx
+ andl $7,%ecx
+ jz 102f /* already aligned */
+ subl $8,%ecx
+ negl %ecx
+ subl %ecx,%edx
+0: movb (%rsi),%al
+ movb %al,(%rdi)
+ incq %rsi
+ incq %rdi
+ decl %ecx
+ jnz 0b
+102:
+ movl %edx,%ecx
+ andl $63,%edx
+ shrl $6,%ecx
+ jz 17f
+1: movq (%rsi),%r8
+2: movq 1*8(%rsi),%r9
+3: movq 2*8(%rsi),%r10
+4: movq 3*8(%rsi),%r11
+ mov %r8,(%rdi)
+ mov %r9,1*8(%rdi)
+ mov %r10,2*8(%rdi)
+ mov %r11,3*8(%rdi)
+9: movq 4*8(%rsi),%r8
+10: movq 5*8(%rsi),%r9
+11: movq 6*8(%rsi),%r10
+12: movq 7*8(%rsi),%r11
+ mov %r8,4*8(%rdi)
+ mov %r9,5*8(%rdi)
+ mov %r10,6*8(%rdi)
+ mov %r11,7*8(%rdi)
+ leaq 64(%rsi),%rsi
+ leaq 64(%rdi),%rdi
+ decl %ecx
+ jnz 1b
+17: movl %edx,%ecx
+ andl $7,%edx
+ shrl $3,%ecx
+ jz 20f
+18: movq (%rsi),%r8
+ mov %r8,(%rdi)
+ leaq 8(%rsi),%rsi
+ leaq 8(%rdi),%rdi
+ decl %ecx
+ jnz 18b
+20: andl %edx,%edx
+ jz 23f
+ movl %edx,%ecx
+21: movb (%rsi),%al
+ movb %al,(%rdi)
+ incq %rsi
+ incq %rdi
+ decl %ecx
+ jnz 21b
+23: xorl %eax,%eax
+ sfence
+ ret
+
+ .section .fixup,"ax"
+30:
+ addl %ecx,%edx
+ jmp 100f
+31:
+ shll $6,%ecx
+ addl %ecx,%edx
+ jmp 100f
+32:
+ shll $6,%ecx
+ leal -8(%ecx,%edx),%edx
+ jmp 100f
+33:
+ shll $6,%ecx
+ leal -16(%ecx,%edx),%edx
+ jmp 100f
+34:
+ shll $6,%ecx
+ leal -24(%ecx,%edx),%edx
+ jmp 100f
+35:
+ shll $6,%ecx
+ leal -32(%ecx,%edx),%edx
+ jmp 100f
+36:
+ shll $6,%ecx
+ leal -40(%ecx,%edx),%edx
+ jmp 100f
+37:
+ shll $6,%ecx
+ leal -48(%ecx,%edx),%edx
+ jmp 100f
+38:
+ shll $6,%ecx
+ leal -56(%ecx,%edx),%edx
+ jmp 100f
+39:
+ lea (%rdx,%rcx,8),%rdx
+ jmp 100f
+40:
+ movl %ecx,%edx
+100:
+ sfence
+ movabsq $0x8000000000000000, %rax
+ orq %rdx,%rax
+ ret
+ .previous
+
+ _ASM_MCEXTABLE(0b,30b)
+ _ASM_MCEXTABLE(1b,31b)
+ _ASM_MCEXTABLE(2b,32b)
+ _ASM_MCEXTABLE(3b,33b)
+ _ASM_MCEXTABLE(4b,34b)
+ _ASM_MCEXTABLE(9b,35b)
+ _ASM_MCEXTABLE(10b,36b)
+ _ASM_MCEXTABLE(11b,37b)
+ _ASM_MCEXTABLE(12b,38b)
+ _ASM_MCEXTABLE(18b,39b)
+ _ASM_MCEXTABLE(21b,40b)
+ENDPROC(mcsafe_memcpy)
--
2.1.4
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