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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 04/25] KVM: x86: Mark CR4.FRED as not reserved
Thread-Topic: [PATCH v2 04/25] KVM: x86: Mark CR4.FRED as not reserved
Thread-Index: AQHaWe+gBPWte0uMqUOIgIdlQKoa17HFZoMAgABotFA=
Date: Thu, 13 Jun 2024 03:27:48 +0000
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References: <20240207172646.3981-1-xin3.li@intel.com>
 <20240207172646.3981-5-xin3.li@intel.com> <ZmoPLOx8sujVsGIS@google.com>
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> On Wed, Feb 07, 2024, Xin Li wrote:
> > The CR4.FRED bit, i.e., CR4[32], is no longer a reserved bit when a gue=
st
> > enumerates FRED, otherwise it is still a reserved bit.
>=20
> This isn't quite correct, as __cr4_reserved_bits() is used with kvm_cpu_c=
aps too,
> i.e. to compute CR4 bits that are reserved from the host's perspective.  =
And that
> matters, because if this check was done _only_ on guest CPUID, then KVM w=
ould
> allow CR4.FRED=3D1 before all of KVM support is in place.

Ah, that means I didn't dig deep enough.

Thanks!
    Xin