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From:   Jim Mattson <jmattson@google.com>
Date:   Mon, 9 Nov 2020 14:36:29 -0800
Message-ID: <CALMp9eTFaiYkTnVe8xKzg40E4nZ3rAOii0O06bTy0+oLNjyKhA@mail.gmail.com>
Subject: Re: [tip: ras/core] x86/mce: Enable additional error logging on
 certain Intel CPUs
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Qian Cai <cai@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tip-commits@vger.kernel.org" 
        <linux-tip-commits@vger.kernel.org>, Boris Petkov <bp@alien8.de>,
        Borislav Petkov <bp@suse.de>, x86 <x86@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
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On Mon, Nov 9, 2020 at 2:09 PM Luck, Tony <tony.luck@intel.com> wrote:
>
> What does KVM do with model specific MSRs?

"Model specific model-specific registers?" :-)

KVM only implements a small subset of MSRs. By default, any access to
the rest raises #GP.

> Looks like you let the guest believe it was running on one of Sandy Bridge, Ivy Bridge, Haswell (Xeon).
>
> So, the core MCE code tried to enable extended error reporting.
>
> If there is a mode to have KVM let the guest think that it read/wrote MSR 0x17F,
> but actually, doesn't do it ... that would seem to be a reasonable thing to do here.

There is an 'ignore_msrs' module parameter, to sink writes and return
zero on reads for unknown MSRs, but I don't think it's commonly used.

I thought Linux had long ago gone the route of turning rdmsr/wrmsr
into rdmsr_safe/wrmsr_safe, so that the guest would ignore the #GPs on
writes and return zero to the caller for #GPs on reads.