linux-kernel - Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

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Message-ID: <X/3jap249oBJ/a6s@google.com>
Date:   Tue, 12 Jan 2021 09:59:06 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Wei Huang <wei.huang2@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, vkuznets@...hat.com, joro@...tes.org,
        bp@...en8.de, tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        jmattson@...gle.com, wanpengli@...cent.com, bsd@...hat.com,
        dgilbert@...hat.com, mlevitsk@...hat.com
Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by
 VM instructions

On Tue, Jan 12, 2021, Sean Christopherson wrote:
> On Tue, Jan 12, 2021, Wei Huang wrote:
> > From: Bandan Das <bsd@...hat.com>
> > 
> > While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD
> > CPUs check EAX against reserved memory regions (e.g. SMM memory on host)
> > before checking VMCB's instruction intercept.
> 
> It would be very helpful to list exactly which CPUs are/aren't affected, even if
> that just means stating something like "all CPUs before XYZ".  Given patch 2/2,
> I assume it's all CPUs without the new CPUID flag?

Ah, despite calling this an 'errata', the bad behavior is explicitly documented
in the APM, i.e. it's an architecture bug, not a silicon bug.

Can you reword the changelog to make it clear that the premature #GP is the
correct architectural behavior for CPUs without the new CPUID flag?