linux-kernel - Re: [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest

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Message-ID: <CALMp9eSSiPVWDf43Zed3+ukUc+NwMP8z7feoxX0eMmimvrznzA@mail.gmail.com>
Date:   Tue, 4 May 2021 14:58:42 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Reiji Watanabe <reijiw@...gle.com>
Subject: Re: [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be
 disabled in the guest

On Tue, May 4, 2021 at 2:57 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 04/05/21 23:53, Sean Christopherson wrote:
> >> Does the right thing happen here if the vCPU is in guest mode when
> >> userspace decides to toggle the CPUID.80000001H:EDX.RDTSCP bit on or
> >> off?
> > I hate our terminology.  By "guest mode", do you mean running the vCPU, or do
> > you specifically mean running in L2?
> >
>
> Guest mode should mean L2.
>
> (I wonder if we should have a capability that says "KVM_SET_CPUID2 can
> only be called prior to KVM_RUN").

It would certainly make it easier to reason about potential security issues.