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Message-ID: <SA1PR11MB67348C0E467D474EF9B38C01A8C12@SA1PR11MB6734.namprd11.prod.outlook.com>
Date: Thu, 13 Jun 2024 03:31:07 +0000
From: "Li, Xin3" <xin3.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
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Subject: RE: [PATCH v2 06/25] KVM: VMX: Defer enabling FRED MSRs save/load
until after set CPUID
> On Wed, Feb 07, 2024, Xin Li wrote:
> > Clear FRED VM entry/exit controls when initializing a vCPU, and set
> > these controls only if FRED is enumerated after set CPUID.
> >
> > FRED VM entry/exit controls need to be set to establish context
> > sufficient to support FRED event delivery immediately after VM entry
> > and exit. However it is not required to save/load FRED MSRs for
> > a non-FRED guest, which aren't supposed to access FRED MSRs.
>
> Does this actually provide a measurable performance boost? If not, just do the
> unnecessary load/store on entry/exit.
No performance measurement yet. Will make the change.
>
> Generally speaking, the only time KVM dynamically toggles entry/exit controls is
> when KVM wants to run the guest with a host value, e.g. with the host's
> PERF_GLOBAL_CTRL.
Simple rule.
Thanks!
Xin
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