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

[Borislav Petkov <bp@alien8.de>]

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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