Re: [PATCH] x86, MCE, AMD: save IA32_MCi_STATUS before machine_check_poll() resets it

Borislav Petkov
2014-09-30T07:25:58Z

On Tue, Sep 30, 2014 at 08:39:38AM +0800, Chen Yucong wrote:
> machine_check_poll() will scan all banks, so I think we can move it out
> of the loop body.

Ok.

> From: Chen Yucong
>
> machine_check_poll() will reset IA32_MCi_STATUS register to zero.
> So we need to save the content of IA32_MCi_STATUS MSRs before
> calling machine_check_poll() for logging threshold interrupt event.
>
> mce_setup() does not gather the content of IA32_MCG_STATUS, so it
> should be read explicitly. And we also need to save MSR_IA32_MCx_ADDR
> if MCI_STATUS_ADDRV bit field is valid.
>
> Signed-off-by: Chen Yucong <slaoub@gmail.com>
> ---
> arch/x86/kernel/cpu/mcheck/mce_amd.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
> index f8c56bd..f5a5beb 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
> @@ -274,6 +274,7 @@ static void amd_threshold_interrupt(void)
> struct mce m;
>
> mce_setup(&m);
> + rdmsrl(MSR_IA32_MCG_STATUS, m.mcgstatus);
>
> /* assume first bank caused it */
> for (bank = 0; bank < mca_cfg.banks; ++bank) {
> @@ -305,24 +306,28 @@ static void amd_threshold_interrupt(void)
> (high & MASK_LOCKED_HI))
> continue;
>
> - /*
> - * Log the machine check that caused the threshold
> - * event.
> - */
> - machine_check_poll(MCP_TIMESTAMP,
> - this_cpu_ptr(&mce_poll_banks));
> -
> if (high & MASK_OVERFLOW_HI) {
> rdmsrl(address, m.misc);
> rdmsrl(MSR_IA32_MCx_STATUS(bank), m.status);
> + if (m.status & MCI_STATUS_ADDRV)
> + rdmsrl(MSR_IA32_MCx_ADDR(bank), m.addr);
> m.bank = K8_MCE_THRESHOLD_BASE
> + bank * NR_BLOCKS
> + block;
> mce_log(&m);
> - return;
> +
> + wrmsrl(MSR_IA32_MCx_STATUS(bank), 0);

No, machine_check_poll will clear it anyway and now you're adding a
purely useless MSR write here which costs.

> + goto log_mcheck;

Why goto? It will hit that machine_check_poll below even without it...

> +
> +log_mcheck:
> + /*
> + * Log the machine check that caused the threshold event.
> + */
> + machine_check_poll(MCP_TIMESTAMP,
> + this_cpu_ptr(&mce_poll_banks));
> }

Of course, the more important question is: how are you testing your patches?

Thanks.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
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