linux-kernel - Re: [PATCH v2 12/12] KVM: x86/pmu: Clear reserved bit PERF

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Date:   Tue, 8 Mar 2022 19:25:47 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/12] KVM: x86/pmu: Clear reserved bit PERF_CTL2[43]
 for AMD erratum 1292

On 5/3/2022 3:06 am, Jim Mattson wrote:
> We should continue to synthesize a #GP for an attempt to set "must be
> zero" bits or for rule violations, like "address must be canonical."

Actually, I do stand in the same position as you.

> However, we have absolutely no business making up our own hardware
> specification. This is a bug, and it should be fixed, like any other
> bug.
Current virtual hardware interfaces do not strictly comply with vendor 
specifications
and may not be the same in the first step of enablement, or some of them may have
to be compromised later out of various complexity.

The behavior of AMD's "synthesize a #GP" to "reserved without qualification" bits
is clearly a legacy tech decision (not sure if it was intentional). We may need 
a larger
independent patch set to apply this one-time surgery, including of course this 
pmu issue.

What do you think ?