Re: [PATCH 1/3] x86, ras: Add new infrastructure for machine check fixup tables

Borislav Petkov
2015-11-10T11:21:31Z

On Fri, Nov 06, 2015 at 12:57:03PM -0800, Tony Luck wrote:
> Copy the existing page fault fixup mechanisms to create a new table
> to be used when fixing machine checks. Note:
> 1) At this time we only provide a macro to annotate assembly code
> 2) We assume all fixups will in code builtin to the kernel.
>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
> arch/x86/include/asm/asm.h | 7 +++++++
> arch/x86/include/asm/uaccess.h | 1 +
> arch/x86/mm/extable.c | 16 ++++++++++++++++
> include/asm-generic/vmlinux.lds.h | 6 ++++++
> include/linux/module.h | 1 +
> kernel/extable.c | 14 ++++++++++++++
> 6 files changed, 45 insertions(+)
>
> diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
> index 189679aba703..f2fa7973f18f 100644
> --- a/arch/x86/include/asm/asm.h
> +++ b/arch/x86/include/asm/asm.h
> @@ -58,6 +58,13 @@
> .long (to) - . + 0x7ffffff0 ; \
> .popsection
>
> +# define _ASM_MCEXTABLE(from, to) \

Maybe add an intermediary macro which abstracts the table name:

#define __ASM_EXTABLE(from, to, table)
...

and then do

#define _ASM_EXTABLE(from, to) __ASM_EXTABLE(from, to, "__ex_table")
#define _ASM_MCEXTABLE(from, to) __ASM_EXTABLE(from, to, "__mcex_table")

> + .pushsection "__mcex_table", "a" ; \
> + .balign 8 ; \
> + .long (from) - . ; \
> + .long (to) - . ; \
> + .popsection
> +
> # define _ASM_NOKPROBE(entry) \
> .pushsection "_kprobe_blacklist","aw" ; \
> _ASM_ALIGN ; \
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index a8df874f3e88..b8231301a224 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -111,6 +111,7 @@ struct exception_table_entry {
> #define ARCH_HAS_SEARCH_EXTABLE
>
> extern int fixup_exception(struct pt_regs *regs);
> +extern int fixup_mcexception(struct pt_regs *regs);
> extern int early_fixup_exception(unsigned long *ip);
>
> /*
> diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
> index 903ec1e9c326..5b328ae00365 100644
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -49,6 +49,22 @@ int fixup_exception(struct pt_regs *regs)
> return 0;
> }
>
> +int fixup_mcexception(struct pt_regs *regs)
> +{
> + const struct exception_table_entry *fixup;
> + unsigned long new_ip;
> +
> + fixup = search_mcexception_tables(regs->ip);
> + if (fixup) {
> + new_ip = ex_fixup_addr(fixup);
> +
> + regs->ip = new_ip;
> + return 1;
> + }
> +
> + return 0;
> +}

Yeah, all that duplication might raise some brows but I'd guess
special-handling MCA in the normal exception paths might make the code
a bit too ugly...

--
Regards/Gruss,
Boris.

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