linux-kernel - Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM

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Message-ID: <ceb63787-b057-13db-4624-b430c51625f1@redhat.com>
Date:   Wed, 5 Jan 2022 10:10:54 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>
Cc:     kvm@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN

On 1/3/22 13:56, Vitaly Kuznetsov wrote:
>   'allowlist' of things which can change (and put
> *APICids there) and only fail KVM_SET_CPUID{,2} when we see something
> else changing.

We could also go the other way and only deny changes that result in 
changed CPU caps.  That should be easier to implement since we have 
already a mapping from CPU capability words to CPUID leaves and registers.

Paolo