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

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Message-ID: <fa16949e-7842-45f7-9715-1bdda13b762a@zytor.com>
Date: Fri, 11 Apr 2025 21:32:32 -0700
From: Xin Li <xin@...or.com>
To: 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,
        xen-devel@...ts.xenproject.org, linux-ide@...r.kernel.org,
        linux-pm@...r.kernel.org, bpf@...r.kernel.org, llvm@...ts.linux.dev,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        jgross@...e.com, andrew.cooper3@...rix.com, peterz@...radead.org,
        acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com,
        wei.liu@...nel.org, ajay.kaher@...adcom.com,
        bcm-kernel-feedback-list@...adcom.com, tony.luck@...el.com,
        pbonzini@...hat.com, vkuznets@...hat.com, luto@...nel.org,
        boris.ostrovsky@...cle.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        decui@...rosoft.com
Subject: Re: [RFC PATCH v1 10/15] KVM: VMX: Use WRMSRNS or its immediate form
 when available

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.