linux-kernel - Re: [PATCH v3 2/2] KVM: SVM: Add support for Virtual SPEC

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Message-ID: <YBCwPHOXgVqnnMQ6@google.com>
Date:   Tue, 26 Jan 2021 16:13:48 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Babu Moger <babu.moger@....com>
Cc:     pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, fenghua.yu@...el.com, tony.luck@...el.com,
        wanpengli@...cent.com, kvm@...r.kernel.org,
        thomas.lendacky@....com, peterz@...radead.org, joro@...tes.org,
        x86@...nel.org, kyung.min.park@...el.com,
        linux-kernel@...r.kernel.org, krish.sadhukhan@...cle.com,
        hpa@...or.com, mgross@...ux.intel.com, vkuznets@...hat.com,
        kim.phillips@....com, wei.huang2@....com, jmattson@...gle.com
Subject: Re: [PATCH v3 2/2] KVM: SVM: Add support for Virtual SPEC_CTRL

On Wed, Jan 20, 2021, Babu Moger wrote:
> 
> On 1/19/21 5:45 PM, Sean Christopherson wrote:

> > Potentially harebrained alternative...
> > 
> > From an architectural SVM perspective, what are the rules for VMCB fields that
> > don't exist (on the current hardware)?  E.g. are they reserved MBZ?  If not,
> > does the SVM architecture guarantee that reserved fields will not be modified?
> > I couldn't (quickly) find anything in the APM that explicitly states what
> > happens with defined-but-not-existent fields.
> 
> I checked with our hardware design team about this. They dont want
> software to make any assumptions about these fields.

Drat, I should have begged for forgiveness instead of asking for permission :-D