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Message-ID: <20160207165524.GF5862@pd.tnic>
Date: Sun, 7 Feb 2016 17:55:24 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tony Luck <tony.luck@...el.com>,
Richard Weinberger <richard@....at>
Cc: Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Dan Williams <dan.j.williams@...el.com>, elliott@....com,
Brian Gerst <brgerst@...il.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-nvdimm@...1.01.org, x86@...nel.org
Subject: Re: [PATCH v10 3/4] x86, mce: Add __mcsafe_copy()
On Fri, Jan 08, 2016 at 01:18:03PM -0800, Tony Luck wrote:
> 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 trapnr;
> u64 remain;
> };
>
> If the copy is successful, then both 'trapnr' and 'remain' are zero.
>
> If we faulted during the copy, then 'trapnr' will say which type
> of trap (X86_TRAP_PF or X86_TRAP_MC) and 'remain' 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.
>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
> arch/x86/include/asm/string_64.h | 8 +++
> arch/x86/kernel/x8664_ksyms_64.c | 2 +
> arch/x86/lib/memcpy_64.S | 134 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 144 insertions(+)
>
> diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
> index ff8b9a17dc4b..5b24039463a4 100644
> --- a/arch/x86/include/asm/string_64.h
> +++ b/arch/x86/include/asm/string_64.h
> @@ -78,6 +78,14 @@ int strcmp(const char *cs, const char *ct);
> #define memset(s, c, n) __memset(s, c, n)
> #endif
>
> +struct mcsafe_ret {
> + u64 trapnr;
> + u64 remain;
> +};
> +
> +struct mcsafe_ret __mcsafe_copy(void *dst, const void __user *src, size_t cnt);
> +extern void __mcsafe_copy_end(void);
> +
> #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..fff245462a8c 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(__mcsafe_copy);
> +
> 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..f576acad485e 100644
> --- a/arch/x86/lib/memcpy_64.S
> +++ b/arch/x86/lib/memcpy_64.S
> @@ -177,3 +177,137 @@ ENTRY(memcpy_orig)
> .Lend:
> retq
> ENDPROC(memcpy_orig)
> +
> +#ifndef CONFIG_UML
So this is because we get a link failure on UML:
arch/x86/um/built-in.o:(__ex_table+0x8): undefined reference to `ex_handler_fault'
arch/x86/um/built-in.o:(__ex_table+0x14): undefined reference to `ex_handler_fault'
arch/x86/um/built-in.o:(__ex_table+0x20): undefined reference to `ex_handler_fault'
arch/x86/um/built-in.o:(__ex_table+0x2c): undefined reference to `ex_handler_fault'
arch/x86/um/built-in.o:(__ex_table+0x38): undefined reference to `ex_handler_fault'
arch/x86/um/built-in.o:(__ex_table+0x44): more undefined references to `ex_handler_fault' follow
collect2: error: ld returned 1 exit status
make: *** [vmlinux] Error 1
due to those
> + _ASM_EXTABLE_FAULT(0b,30b)
> + _ASM_EXTABLE_FAULT(1b,31b)
> + _ASM_EXTABLE_FAULT(2b,32b)
> + _ASM_EXTABLE_FAULT(3b,33b)
> + _ASM_EXTABLE_FAULT(4b,34b)
things below and that's because ex_handler_fault() is defined in
arch/x86/mm/extable.c and UML doesn't include that file in the build. It
takes kernel/extable.c and lib/extable.c only.
Richi, what's the usual way to address that in UML? I.e., make an
x86-only symbol visible to the UML build too? Define a dummy one, just
so that it builds?
> + * __mcsafe_copy - 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_copy)
> + 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: xorq %rax, %rax
> + xorq %rdx, %rdx
> + /* copy successful. return 0 */
> + ret
> +
> + .section .fixup,"ax"
> + /*
> + * machine check handler loaded %rax with trap number
> + * We just need to make sure %edx has the number of
> + * bytes remaining
> + */
> +30:
> + add %ecx,%edx
> + ret
> +31:
> + shl $6,%ecx
> + add %ecx,%edx
> + ret
> +32:
> + shl $6,%ecx
> + lea -8(%ecx,%edx),%edx
> + ret
> +33:
> + shl $6,%ecx
> + lea -16(%ecx,%edx),%edx
> + ret
> +34:
> + shl $6,%ecx
> + lea -24(%ecx,%edx),%edx
> + ret
> +35:
> + shl $6,%ecx
> + lea -32(%ecx,%edx),%edx
> + ret
> +36:
> + shl $6,%ecx
> + lea -40(%ecx,%edx),%edx
> + ret
> +37:
> + shl $6,%ecx
> + lea -48(%ecx,%edx),%edx
> + ret
> +38:
> + shl $6,%ecx
> + lea -56(%ecx,%edx),%edx
> + ret
> +39:
> + lea (%rdx,%rcx,8),%rdx
> + ret
> +40:
> + mov %ecx,%edx
> + ret
> + .previous
> +
> + _ASM_EXTABLE_FAULT(0b,30b)
> + _ASM_EXTABLE_FAULT(1b,31b)
> + _ASM_EXTABLE_FAULT(2b,32b)
> + _ASM_EXTABLE_FAULT(3b,33b)
> + _ASM_EXTABLE_FAULT(4b,34b)
> + _ASM_EXTABLE_FAULT(9b,35b)
> + _ASM_EXTABLE_FAULT(10b,36b)
> + _ASM_EXTABLE_FAULT(11b,37b)
> + _ASM_EXTABLE_FAULT(12b,38b)
> + _ASM_EXTABLE_FAULT(18b,39b)
> + _ASM_EXTABLE_FAULT(21b,40b)
> +#endif
> --
> 2.5.0
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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