linux-kernel - Re: [PATCH] proc: added ept

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Message-ID: <alpine.DEB.2.21.1808031158400.1745@nanos.tec.linutronix.de>
Date:   Fri, 3 Aug 2018 12:02:01 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Shier <pshier@...gle.com>
cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org, bp@...e.de,
        konrad.wilk@...cle.com, dwmw@...zon.co.uk,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, Peter Feiner <pfeiner@...gle.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH] proc: added ept_ad flag to /proc/cpuinfo

Peter,

On Thu, 2 Aug 2018, Peter Shier wrote:
> Thank you Thomas. I missed what I think is your fundamental point
> regarding duplication created by this patch between CPU feature bits
> and KVM's consumption of the IA32_VMX_EPT_VPID_CAP MSR.
> 
> Should all the features in this MSR be exposed via CPU feature bits
> and should KVM consume only from there rather than reading the MSR
> directly? There are 16 feature bits in the MSR per SDM Vol 3d section
> A.10.

Uuurg. Probably not, unless they are important somehow for similar reasons
like the one you are exposing. I assume they are not, so using the MSR and
picking all bits directly from there is ok.

But thanks for taking a look as noew we at least know why it doesn't make
sense to convert VMX over as it has to read the MSR anyway.

Thanks,

	tglx