linux-kernel - Re: [PATCH 02/15] KVM: x86: Emulate RDPID only if RDTSCP is supported

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Date:   Tue, 4 May 2021 10:50:10 -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 02/15] KVM: x86: Emulate RDPID only if RDTSCP is supported

On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Do not advertise emulation support for RDPID if RDTSCP is unsupported.
> RDPID emulation subtly relies on MSR_TSC_AUX to exist in hardware, as
> both vmx_get_msr() and svm_get_msr() will return an error if the MSR is
> unsupported, i.e. ctxt->ops->get_msr() will fail and the emulator will
> inject a #UD.
>
> Note, RDPID emulation also relies on RDTSCP being enabled in the guest,
> but this is a KVM bug and will eventually be fixed.
>
> Fixes: fb6d4d340e05 ("KVM: x86: emulate RDPID")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed by: Jim Mattson <jmattson@...gle.com>