Re: [PATCH 2/3] x86, ras: Extend machine check recovery code to annotated ring0 areas

[Borislav Petkov <bp@alien8.de>]

On Fri, Nov 06, 2015 at 01:01:55PM -0800, Tony Luck wrote:
> Extend the severity checking code to add a new context IN_KERN_RECOV
> which is used to indicate that the machine check was triggered by code
> in the kernel with a fixup entry.
> 
> Add code to check for this situation and respond by altering the return
> IP to the fixup address and changing the regs->ax so that the recovery
> code knows the physical address of the error. Note that we also set bit
> 63 because 0x0 is a legal physical address.
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>  arch/x86/kernel/cpu/mcheck/mce-severity.c | 19 +++++++++++++++++--
>  arch/x86/kernel/cpu/mcheck/mce.c          | 13 ++++++++++---
>  2 files changed, 27 insertions(+), 5 deletions(-)

...

> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 9d014b82a124..472d11150b7a 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -31,6 +31,7 @@
>  #include <linux/types.h>
>  #include <linux/slab.h>
>  #include <linux/init.h>
> +#include <linux/module.h>
>  #include <linux/kmod.h>
>  #include <linux/poll.h>
>  #include <linux/nmi.h>
> @@ -1132,9 +1133,15 @@ void do_machine_check(struct pt_regs *regs, long error_code)

You could save a precious indentation level here:

	if (cfg->tolerant == 3)
		goto clear;

and add the "clear" label below.

clear:
        if (worst > 0)
                mce_report_event(regs);
        mce_wrmsrl(MSR_IA32_MCG_STATUS, 0)

>  		if (no_way_out)
>  			mce_panic("Fatal machine check on current CPU", &m, msg);
>  		if (worst == MCE_AR_SEVERITY) {
> -			recover_paddr = m.addr;
> -			if (!(m.mcgstatus & MCG_STATUS_RIPV))
> -				flags |= MF_MUST_KILL;
> +			if ((m.cs & 3) == 3) {
> +				recover_paddr = m.addr;
> +				if (!(m.mcgstatus & MCG_STATUS_RIPV))
> +					flags |= MF_MUST_KILL;
> +			} else if (fixup_mcexception(regs)) {
> +				regs->ax = BIT(63) | m.addr;
> +			} else
> +				mce_panic("Failed kernel mode recovery",
> +					  &m, NULL);
>  		} else if (kill_it) {
>  			force_sig(SIGBUS, current);
>  		}
> -- 
> 2.1.4
> 
> 

-- 
Regards/Gruss,
    Boris.

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