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Date: Fri, 19 Feb 2016 09:53:53 -0800
From: "Luck, Tony" <tony.luck@...el.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH v13] x86, mce: Add memcpy_trap()
Make use of the EXTABLE_FAULT exception table entries. This routine
returns a structure to indicate the result of the copy:
struct mcsafe_ret {
u64 trap_nr;
u64 bytes_left;
};
If the copy is successful, then both 'trap_nr' and 'bytes_left' are zero.
If we faulted during the copy, then 'trap_nr' will say which type
of trap (X86_TRAP_PF or X86_TRAP_MC) and 'bytes_left' says how many
bytes were not copied.
Note that this is probably the first of several copy functions.
We can make new ones for non-temporal cache handling etc.
Reviewed-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Tony Luck <tony.luck@...el.com>
---
V12-V13
Ingo: Separate instruction arguments with a ", "
Note that I didn't add spaces after "," within an argument.
E.g. "lea (%rdx,%rcx,8), %rdx"
Did you want them there too? I don't think they help as much there.
Ingo: More readable layout for fixup stubs
arch/x86/include/asm/string_64.h | 26 ++++++++
arch/x86/kernel/x8664_ksyms_64.c | 2 +
arch/x86/lib/memcpy_64.S | 128 +++++++++++++++++++++++++++++++++++++++
3 files changed, 156 insertions(+)
diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index ff8b9a17dc4b..65e5793b7590 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -78,6 +78,32 @@ int strcmp(const char *cs, const char *ct);
#define memset(s, c, n) __memset(s, c, n)
#endif
+/**
+ * struct memcpy_trap_ret - return value from memcpy_trap()
+ *
+ * @trap_nr x86 trap number if the copy failed
+ * @bytes_left zero for successful copy else number of bytes not copied
+ */
+struct memcpy_trap_ret {
+ u64 trap_nr;
+ u64 bytes_left;
+};
+
+/**
+ * memcpy_trap - copy memory with indication if a trap interrupted the copy
+ *
+ * @dst: destination address
+ * @src: source address
+ * @cnt: number of bytes to copy
+ *
+ * Low level memory copy function that catches traps and indicates whether
+ * the copy succeeded and if not, why it failed.
+ *
+ * Return is struct memcpy_trap_ret which provides both the number of bytes
+ * not copied and the reason for the failure.
+ */
+struct memcpy_trap_ret memcpy_trap(void *dst, const void __user *src, size_t cnt);
+
#endif /* __KERNEL__ */
#endif /* _ASM_X86_STRING_64_H */
diff --git a/arch/x86/kernel/x8664_ksyms_64.c b/arch/x86/kernel/x8664_ksyms_64.c
index a0695be19864..40866e2cbcc4 100644
--- a/arch/x86/kernel/x8664_ksyms_64.c
+++ b/arch/x86/kernel/x8664_ksyms_64.c
@@ -37,6 +37,8 @@ EXPORT_SYMBOL(__copy_user_nocache);
EXPORT_SYMBOL(_copy_from_user);
EXPORT_SYMBOL(_copy_to_user);
+EXPORT_SYMBOL_GPL(memcpy_trap);
+
EXPORT_SYMBOL(copy_page);
EXPORT_SYMBOL(clear_page);
diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index 16698bba87de..b8dccda0575d 100644
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -177,3 +177,131 @@ ENTRY(memcpy_orig)
.Lend:
retq
ENDPROC(memcpy_orig)
+
+#ifndef CONFIG_UML
+/*
+ * memcpy_trap - 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_trap)
+ cmpl $8, %edx
+ /* Less than 8 bytes? Go to byte copy loop */
+ jb .L_no_whole_words
+
+ /* Check for bad alignment of source */
+ testl $7, %esi
+ /* Already aligned */
+ jz .L_8byte_aligned
+
+ /* Copy one byte at a time until source is 8-byte aligned */
+ movl %esi, %ecx
+ andl $7, %ecx
+ subl $8, %ecx
+ negl %ecx
+ subl %ecx, %edx
+.L_copy_leading_bytes:
+ movb (%rsi), %al
+ movb %al, (%rdi)
+ incq %rsi
+ incq %rdi
+ decl %ecx
+ 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:
+ movq (%rsi), %r8
+ mov %r8, (%rdi)
+ leaq 8(%rsi), %rsi
+ leaq 8(%rdi), %rdi
+ decl %ecx
+ jnz .L_copy_trailing_words
+
+ /* Any trailing bytes? */
+.L_no_whole_words:
+ andl %edx, %edx
+ jz .L_done_memcpy_trap
+
+ /* Copy trailing bytes */
+ movl %edx, %ecx
+.L_copy_trailing_bytes:
+ movb (%rsi), %al
+ movb %al, (%rdi)
+ incq %rsi
+ incq %rdi
+ decl %ecx
+ jnz .L_copy_trailing_bytes
+
+ /* Copy successful. Return .remain = 0, .trapnr = 0 */
+.L_done_memcpy_trap:
+ xorq %rax, %rax
+ xorq %rdx, %rdx
+ ret
+
+ .section .fixup, "ax"
+ /*
+ * The machine check handler loaded %rax with trap number.
+ * We just need to make sure %edx has the number of
+ * bytes remaining.
+ */
+.L_fix_leading_bytes: add %ecx, %edx; ret
+.L_fix_cache_w0: shl $6, %ecx; add %ecx, %edx; ret
+.L_fix_cache_w1: shl $6, %ecx; lea -8(%ecx,%edx), %edx; ret
+.L_fix_cache_w2: shl $6, %ecx; lea -16(%ecx,%edx), %edx; ret
+.L_fix_cache_w3: shl $6, %ecx; lea -24(%ecx,%edx), %edx; ret
+.L_fix_cache_w4: shl $6, %ecx; lea -32(%ecx,%edx), %edx; ret
+.L_fix_cache_w5: shl $6, %ecx; lea -40(%ecx,%edx), %edx; ret
+.L_fix_cache_w6: shl $6, %ecx; lea -48(%ecx,%edx), %edx; ret
+.L_fix_cache_w7: shl $6, %ecx; lea -56(%ecx,%edx), %edx; ret
+.L_fix_trailing_words: lea (%rdx,%rcx,8), %rdx; ret
+.L_fix_trailing_bytes: mov %ecx, %edx; ret
+ .previous
+
+ _ASM_EXTABLE_FAULT(.L_copy_leading_bytes, .L_fix_leading_bytes)
+ _ASM_EXTABLE_FAULT(.L_cache_w0, .L_fix_cache_w0)
+ _ASM_EXTABLE_FAULT(.L_cache_w1, .L_fix_cache_w1)
+ _ASM_EXTABLE_FAULT(.L_cache_w3, .L_fix_cache_w2)
+ _ASM_EXTABLE_FAULT(.L_cache_w3, .L_fix_cache_w3)
+ _ASM_EXTABLE_FAULT(.L_cache_w4, .L_fix_cache_w4)
+ _ASM_EXTABLE_FAULT(.L_cache_w5, .L_fix_cache_w5)
+ _ASM_EXTABLE_FAULT(.L_cache_w6, .L_fix_cache_w6)
+ _ASM_EXTABLE_FAULT(.L_cache_w7, .L_fix_cache_w7)
+ _ASM_EXTABLE_FAULT(.L_copy_trailing_words, .L_fix_trailing_words)
+ _ASM_EXTABLE_FAULT(.L_copy_trailing_bytes, .L_fix_trailing_bytes)
+#endif
--
2.5.0
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