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

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Date:   Mon, 10 May 2021 11:08:34 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>,
        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, 2021-05-04 at 14:58 -0700, Jim Mattson wrote:
> 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.
> 
I vote too for this.
Best regards,
	Maxim Levitsky