linux-kernel - Re: [RFC PATCH v1 10/15] KVM: VMX: Use WRMSRNS or its immediate form when available

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Message-ID: <D212FABE-38FE-45D3-A082-CA819CCFFF95@zytor.com>
Date: Mon, 14 Apr 2025 23:56:47 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Xin Li <xin@...or.com>, Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
CC: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-hyperv@...r.kernel.org, virtualization@...ts.linux.dev,
        linux-edac@...r.kernel.org, kvm@...r.kernel.org,
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Subject: Re: [RFC PATCH v1 10/15] KVM: VMX: Use WRMSRNS or its immediate form when available

On April 14, 2025 10:48:47 AM PDT, Xin Li <xin@...or.com> 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.