linux-kernel - Re: [PATCH v2 0/2] INVD intercept change to skip instruction

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Message-ID: <e8aa489b-493c-87d2-3d26-a34d6eef810f@redhat.com>
Date:   Fri, 25 Sep 2020 19:31:11 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     kvm list <kvm@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 0/2] INVD intercept change to skip instruction

On 24/09/20 23:20, Jim Mattson wrote:
> On Thu, Sep 24, 2020 at 11:42 AM Tom Lendacky <thomas.lendacky@....com> wrote:
>>
>> From: Tom Lendacky <thomas.lendacky@....com>
>>
>> This series updates the INVD intercept support for both SVM and VMX to
>> skip the instruction rather than emulating it, since emulation of this
>> instruction is just a NOP.
> 
> Isn't INVD a serializing instruction, whereas NOP isn't? IIRC, Intel
> doesn't architect VM-entry or VM-exit as serializing, though they
> probably are in practice. I'm not sure what AMD's stance on this is.

Of course that isn't changed by this patch, though.

Queuing both, but a clarification would be useful.  The same applies
even to CPUID.

Paolo