linux-kernel - Re: [PATCH 1/3] KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi

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Date:   Thu, 12 May 2022 15:43:38 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jue Wang <juew@...gle.com>
Subject: Re: [PATCH 1/3] KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi_CTL/STATUS)

On Thu, May 12, 2022 at 3:27 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Return '1', not '-1', when handling an illegal WRMSR to a MCi_CTL or
> MCi_STATUS MSR.  The behavior of "all zeros' or "all ones" for CTL MSRs
> is architectural, as is the "only zeros" behavior for STATUS MSRs.  I.e.
> the intent is to inject a #GP, not exit to userspace due to an unhandled
> emulation case.  Returning '-1' gets interpreted as -EPERM up the stack
> and effecitvely kills the guest.
>
> Fixes: 890ca9aefa78 ("KVM: Add MCE support")
> Fixes: 9ffd986c6e4e ("KVM: X86: #GP when guest attempts to write MCi_STATUS register w/o 0")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
Reviewed-by: Jim Mattson <jmattson@...gle.com>