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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: Sat, 12 Apr 2025 16:10:06 -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: Sat, 12 Apr 2025 23:11:41 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On April 11, 2025 9:32:32 PM PDT, Xin Li <xin@xxxxxxxxx> wrote:
>On 4/11/2025 2:12 PM, Jim Mattson wrote:
>> Surely, any CPU that has WRMSRNS also supports "Virtualize
>> IA32_SPEC_CTRL," right? Shouldn't we be using that feature rather than
>> swapping host and guest values with some form of WRMSR?
>
>Good question, the simple answer is that they are irrelevant.
Also, *in this specific case* IA32_SPEC_CTRL is architecturally nonserializing,
i.e. WRMSR executes as WRMSRNS anyway.
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