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From: "Li, Xin3" <xin3.li@intel.com>
To: Sean Christopherson <seanjc@google.com>
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Subject: RE: [PATCH v2 06/25] KVM: VMX: Defer enabling FRED MSRs save/load
 until after set CPUID
Thread-Topic: [PATCH v2 06/25] KVM: VMX: Defer enabling FRED MSRs save/load
 until after set CPUID
Thread-Index: AQHaWe/CSy+dhNd+hUmy6f2DmzWA2rHFaGsAgABnWRA=
Date: Thu, 13 Jun 2024 03:31:07 +0000
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References: <20240207172646.3981-1-xin3.li@intel.com>
 <20240207172646.3981-7-xin3.li@intel.com> <ZmoQxjksn5bWhlBA@google.com>
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> 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.
>=20
> 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.

>=20
> Generally speaking, the only time KVM dynamically toggles entry/exit cont=
rols 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