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From: Paolo Bonzini <>
To: Sean Christopherson <>,
	Xiaoyao Li <>
Cc: "Radim Krčmář" <>,
	"Thomas Gleixner" <>,
	"Ingo Molnar" <>,
	"Borislav Petkov" <>,
	"H. Peter Anvin" <>,,,
Subject: Re: [PATCH] kvm/x86/vmx: Make the emulation of MSR_IA32_ARCH_CAPABILITIES only for vmx
Date: Thu, 7 Mar 2019 19:15:44 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 07/03/19 18:37, Sean Christopherson wrote:
> On Thu, Mar 07, 2019 at 05:31:43PM +0800, Xiaoyao Li wrote:
>> At present, we report F(ARCH_CAPABILITIES) for x86 arch(both vmx and svm)
>> unconditionally, but we only emulate this MSR in vmx. It will cause #GP
>> while guest kernel rdmsr(MSR_IA32_ARCH_CAPABILITIES) in an AMD host.
>> Since MSR IA32_ARCH_CAPABILITIES is an intel-specific MSR, it makes no
>> sense to emulate it in svm. Thus this patch chooses to only emulate it
>> for vmx, and moves the related handling to vmx related files.
> What about emulating the MSR on an AMD host for testing purpsoes?  It
> might be a useful way for someone without Intel hardware to test spectre
> related flows.
> In other words, an alternative to restricting emulation of the MSR to
> Intel CPUS would be to move MSR_IA32_ARCH_CAPABILITIES handling into
> kvm_{get,set}_msr_common().  Guest access to MSR_IA32_ARCH_CAPABILITIES
> is gated by X86_FEATURE_ARCH_CAPABILITIES in the guest's CPUID, e.g.
> RDMSR will naturally #GP fault if userspace passes through the host's
> CPUID on a non-Intel system.

This is also better because it wouldn't change the guest ABI for AMD
processors.  Dropping CPUID flags is generally not a good idea.


  parent reply	other threads:[~2019-03-07 18:15 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-07  9:31 [PATCH] kvm/x86/vmx: Make the emulation of MSR_IA32_ARCH_CAPABILITIES only for vmx Xiaoyao Li
     [not found] ` <>
2019-03-07 18:15   ` Paolo Bonzini [this message]
2019-03-08  1:53     ` Xiaoyao Li

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