linux-kernel - Re: [PATCH] x86/mce: Keep quiet in case of broadcasted mce after system panic

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Date:   Fri, 17 Feb 2017 09:53:21 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Borislav Petkov <bp@...en8.de>, xlpang@...hat.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, Tony Luck <tony.luck@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Dave Young <dyoung@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>,
        Kiyoshi Ueda <k-ueda@...jp.nec.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/mce: Keep quiet in case of broadcasted mce after
 system panic

On 02/16/2017 at 08:22 PM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 07:52:09PM +0800, Xunlei Pang wrote:
>>     then mce will be broadcast to the other cpus which are still running
>>     in the first kernel(i.e. looping in crash_nmi_callback).
> Simple: the crash code should really mark CPUs as not being online:
>
> void do_machine_check(struct pt_regs *regs, long error_code)
>
> 	...
>
>         /* If this CPU is offline, just bail out. */
>         if (cpu_is_offline(smp_processor_id())) {
>                 u64 mcgstatus;
>
>                 mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
>                 if (mcgstatus & MCG_STATUS_RIPV) {
>                         mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
>                         return;
>                 }
>         }
>
> because looping in crash_nmi_callback() does not really denote them as
> CPUs being online.
>
> And just so that you don't disturb the machine too much during crashing,
> you could simply clear them from the online masks, i.e., perhaps call
> remove_cpu_from_maps() with the proper locking around it instead of
> doing a full cpu_down().

It changes the value of cpu_online_mask/etc which will cause confusion to vmcore analysis.
Moreover, for the code(see comment inlined)

        if (cpu_is_offline(smp_processor_id())) {
                u64 mcgstatus;

                mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
                if (mcgstatus & MCG_STATUS_RIPV) { // This condition may be not true, the mce triggered on kdump cpu 
                                                                     // doesn't need to have this bit set for the other cpus remain in 1st kernel. 
                        mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
                        return;
                }
        }


Regards,
Xunlei

>
> The machine will be killed anyway after kdump is done writing out
> memory.
>