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

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Date:   Tue, 21 Feb 2017 18:20:19 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "xlpang@...hat.com" <xlpang@...hat.com>,
        Borislav Petkov <bp@...en8.de>
CC:     Prarit Bhargava <prarit@...hat.com>,
        Kiyoshi Ueda <k-ueda@...jp.nec.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH] x86/mce: Keep quiet in case of broadcasted mce after
 system panic

> It's from my understanding, I didn't get the explicit description from the intel SDM on this point.
> If a broadcast SRAO comes on real hardware, will MSR_IA32_MCG_STATUS of each cpu have MCG_STATUS_RIPV bit set?

MCG_STATUS is a per-thread MSR and will contain the status appropriate for that thread when #MC is delivered.
So the RIPV bit will be set if, and only if, the thread saved a valid return address for this exception. The net result
is that it is almost always set for "innocent bystander" CPUs that were dragged into the exception handler because
of a broadcast #MC. We make the test because if it isn't set, then the do_machine_check() had better not return
because we have no idea where it will return to - since there is not a valid return IP.

-Tony