linux-kernel - Re: [PATCH v2 5/6] KVM/nVMX: Set the CPU_BASED_USE_MSR_BITMAPS if we have a valid L02 MSR bitmap

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Date:   Sun, 11 Feb 2018 11:19:24 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     tglx@...utronix.de, karahmed@...zon.de, sironi@...zon.de,
        x86@...nel.org, kvm@...r.kernel.org, torvalds@...ux-foundation.org,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org, bp@...en8.de,
        peterz@...radead.org, jmattson@...gle.com, rkrcmar@...hat.com,
        arjan.van.de.ven@...el.com, dave.hansen@...el.com
Subject: Re: [PATCH v2 5/6] KVM/nVMX: Set the CPU_BASED_USE_MSR_BITMAPS if we
 have a valid L02 MSR bitmap


* David Woodhouse <dwmw@...zon.co.uk> wrote:

> From: KarimAllah Ahmed <karahmed@...zon.de>
> 
> We either clear the CPU_BASED_USE_MSR_BITMAPS and end up intercepting all
> MSR accesses or create a valid L02 MSR bitmap and use that. This decision
> has to be made every time we evaluate whether we are going to generate the
> L02 MSR bitmap.
> 
> Before commit 086e7d4118cc ("KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL")
> this was probably OK since the decision was always identical. This is no
> longer the case now since the MSR bitmap might actually change once we
> decide to not intercept SPEC_CTRL and PRED_CMD.

Note, I fixed the changelog to refer to the correct upstream SHA1, which is:

  d28b387fb74d: KVM/VMX: Allow direct access to MSR_IA32_SPEC_CTRL

Thanks,

	Ingo