Re: [PATCH] KVM: VMX: expose the host's ARCH_CAPABILITIES MSR to userspace

[Paolo Bonzini]

On 07/03/2018 15:56, Radim KrÄmÃÅ 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