linux-kernel - Re: [PATCH 01/15] KVM: VMX: Do not adverise RDPID if ENABLE

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Message-ID: <CALMp9eQEP32pqFMtn2WZy1B_Aq1x-J52WhF2tC0dNd0vrdhmPg@mail.gmail.com>
Date:   Tue, 4 May 2021 10:53:06 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.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 01/15] KVM: VMX: Do not adverise RDPID if ENABLE_RDTSCP
 control is unsupported

On Tue, May 4, 2021 at 10:37 AM Jim Mattson <jmattson@...gle.com> wrote:
>
> On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
> > unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
> > bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
> > if ENABLE_RDTSCP is not enabled.
> >
> > Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>
> But KVM will happily emulate RDPID if the instruction causes a #UD
> VM-exit, won't it? See commit fb6d4d340e05 (KVM: x86: emulate RDPID).

Oh, after reading the second patch, I now see why this is needed.

You mispelled 'advertise' in the summary line.

Reviewed-by: Jim Mattson <jmattson@...gle.com>