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From: Jim Mattson <jmattson@google.com>
To: Babu Moger <babu.moger@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"Yu, Fenghua" <fenghua.yu@intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	kvm list <kvm@vger.kernel.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Sean Christopherson <seanjc@google.com>,
	Joerg Roedel <joro@8bytes.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	kyung.min.park@intel.com, LKML <linux-kernel@vger.kernel.org>,
	Krish Sadhukhan <krish.sadhukhan@oracle.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	mgross@linux.intel.com, Vitaly Kuznetsov <vkuznets@redhat.com>,
	kim.phillips@amd.com, wei.huang2@amd.com
Subject: Re: [PATCH 1/2] x86/cpufeatures: Add the Virtual SPEC_CTRL feature
Date: Wed, 9 Dec 2020 15:11:15 -0800	[thread overview]
Message-ID: <CALMp9eRzYoVqr0zm60+pkJbGF+t0ry8k7y=X=R1paDhUUPSVCw@mail.gmail.com> (raw)
In-Reply-To: <2e929c9a-9da9-e7da-9fd4-8e0ea2163a19@amd.com>

On Wed, Dec 9, 2020 at 2:39 PM Babu Moger <babu.moger@amd.com> wrote:
>
>
>
> On 12/7/20 5:22 PM, Jim Mattson wrote:
> > On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@amd.com> wrote:
> >>
> >> Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL
> >> MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present,
> >> the SPEC_CTRL MSR is automatically virtualized and no longer requires
> >> hypervisor intervention.
> >>
> >> Signed-off-by: Babu Moger <babu.moger@amd.com>
> >> ---
> >>  arch/x86/include/asm/cpufeatures.h |    1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> >> index dad350d42ecf..d649ac5ed7c7 100644
> >> --- a/arch/x86/include/asm/cpufeatures.h
> >> +++ b/arch/x86/include/asm/cpufeatures.h
> >> @@ -335,6 +335,7 @@
> >>  #define X86_FEATURE_AVIC               (15*32+13) /* Virtual Interrupt Controller */
> >>  #define X86_FEATURE_V_VMSAVE_VMLOAD    (15*32+15) /* Virtual VMSAVE VMLOAD */
> >>  #define X86_FEATURE_VGIF               (15*32+16) /* Virtual GIF */
> >> +#define X86_FEATURE_V_SPEC_CTRL                (15*32+20) /* Virtual SPEC_CTRL */
> >
> > Shouldn't this bit be reported by KVM_GET_SUPPORTED_CPUID when it's
> > enumerated on the host?
>
> Jim, I am not sure if this needs to be reported by
> KVM_GET_SUPPORTED_CPUID. I dont see V_VMSAVE_VMLOAD or VGIF being reported
> via KVM_GET_SUPPORTED_CPUID. Do you see the need for that?

Every little bit helps. No, it isn't *needed*. But then again, this
entire patchset isn't *needed*, is it?

  reply	other threads:[~2020-12-09 23:12 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-07 22:37 [PATCH 0/2] x86: Add the feature Virtual SPEC_CTRL Babu Moger
2020-12-07 22:37 ` [PATCH 1/2] x86/cpufeatures: Add the Virtual SPEC_CTRL feature Babu Moger
2020-12-07 23:22   ` Jim Mattson
2020-12-09 22:39     ` Babu Moger
2020-12-09 23:11       ` Jim Mattson [this message]
2020-12-22 16:14         ` Babu Moger
2020-12-22 17:41           ` Sean Christopherson
2020-12-22 18:07             ` Babu Moger
2020-12-07 22:37 ` [PATCH 2/2] KVM: SVM: Add support for Virtual SPEC_CTRL Babu Moger
2020-12-07 23:06   ` Jim Mattson
2020-12-10 21:26     ` Babu Moger
2020-12-10 21:36       ` Jim Mattson
2020-12-10 22:57         ` Babu Moger
2020-12-22 16:14     ` Babu Moger
2020-12-07 23:13   ` Sean Christopherson
2020-12-10 21:31     ` Babu Moger

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