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Subject: Re: [PATCH] KVM: VMX: expose the host's ARCH_CAPABILITIES MSR to
 userspace
To:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        David Woodhouse <dwmw@amazon.co.uk>,
        KarimAllah Ahmed <karahmed@amazon.de>
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <37a89c09-e933-9256-1b7a-3a9df846a672@redhat.com>
Date:   Wed, 7 Mar 2018 16:10:11 +0100
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On 07/03/2018 15:56, Radim Krčmář wrote:
> The MSR_F10H_DECFG default is questionable -- MSR_F10H_DECFG is an
> architectural MSR, so we'd be changing the guest under the sight of
> existing userspaces.
> A potential security risk if they migrate the guest to a CPU that
> doesn't serialize LFENCE.  ARCH_CAPABILITIES are at least hidden by a
> new CPUID bit.

Good point.  Perhaps we should add a KVM-specific CPUID bit for
serializing LFENCE.

> The feature MSR defaults are going to be a mess anyway: we have
> MSR_IA32_UCODE_REV that is tightly coupled with CPUID.  Not a good
> candidate for passing by default and currently also has a default value.

Yeah, ucode revision is out of question.

Paolo