linux-kernel - Re: [PATCH 03/43] KVM: SVM: Require exact CPUID.0x1 match when stuffing EDX at INIT

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Message-ID: <CAAeT=FyD1ueKWW9h9TBwr_WJNmpb0=9z6rrsyP0u3T=g8UNNfw@mail.gmail.com>
Date:   Tue, 18 May 2021 22:30:46 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/43] KVM: SVM: Require exact CPUID.0x1 match when
 stuffing EDX at INIT

On Fri, Apr 23, 2021 at 5:47 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Do not allow an inexact CPUID "match" when querying the guest's CPUID.0x1
> to stuff EDX during INIT.  In the common case, where the guest CPU model
> is an AMD variant, allowing an inexact match is a nop since KVM doesn't
> emulate Intel's goofy "out-of-range" logic for AMD and Hygon.  If the
> vCPU model happens to be an Intel variant, an inexact match is possible
> if and only if the max CPUID leaf is precisely '0'. Aside from the fact
> that there's probably no CPU in existence with a single CPUID leaf, if
> the max CPUID leaf is '0', that means that CPUID.0.EAX is '0', and thus
> an inexact match for CPUID.0x1.EAX will also yield '0'.
>
> So, with lots of twisty logic, no functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Reiji Watanabe <reijiw@...gle.com>