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Re: [RFC PATCH v1 10/15] KVM: VMX: Use WRMSRNS or its immediate form when available
- To: Xin Li <xin@xxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Mon, 14 Apr 2025 23:56:47 -0700
- Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-perf-users@xxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxx, linux-edac@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-ide@xxxxxxxxxxxxxxx, linux-pm@xxxxxxxxxxxxxxx, bpf@xxxxxxxxxxxxxxx, llvm@xxxxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx, mingo@xxxxxxxxxx, bp@xxxxxxxxx, dave.hansen@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, jgross@xxxxxxxx, andrew.cooper3@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, acme@xxxxxxxxxx, namhyung@xxxxxxxxxx, mark.rutland@xxxxxxx, alexander.shishkin@xxxxxxxxxxxxxxx, jolsa@xxxxxxxxxx, irogers@xxxxxxxxxx, adrian.hunter@xxxxxxxxx, kan.liang@xxxxxxxxxxxxxxx, wei.liu@xxxxxxxxxx, ajay.kaher@xxxxxxxxxxxx, bcm-kernel-feedback-list@xxxxxxxxxxxx, tony.luck@xxxxxxxxx, pbonzini@xxxxxxxxxx, vkuznets@xxxxxxxxxx, luto@xxxxxxxxxx, boris.ostrovsky@xxxxxxxxxx, kys@xxxxxxxxxxxxx, haiyangz@xxxxxxxxxxxxx, decui@xxxxxxxxxxxxx
- Delivery-date: Tue, 15 Apr 2025 06:57:44 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On April 14, 2025 10:48:47 AM PDT, Xin Li <xin@xxxxxxxxx> wrote:
>On 4/12/2025 4:10 PM, H. Peter Anvin wrote:
>> Also,*in this specific case* IA32_SPEC_CTRL is architecturally
>> nonserializing, i.e. WRMSR executes as WRMSRNS anyway.
>
>While the immediate form WRMSRNS could be faster because the MSR index
>is available *much* earlier in the pipeline, right?
Yes, but then it would be redundant with the virtualization support.
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