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From: "Li, Xin3" <xin3.li@intel.com>
To: "Gao, Chao" <chao.gao@intel.com>
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Subject: RE: [PATCH v2 11/25] KVM: x86: Add kvm_is_fred_enabled()
Thread-Topic: [PATCH v2 11/25] KVM: x86: Add kvm_is_fred_enabled()
Thread-Index: AQHaWfAO0doE8sIK3Eq6W5ZDZAAx+7F/aX4AgBE3YdA=
Date: Sat, 11 May 2024 01:24:12 +0000
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References: <20240207172646.3981-1-xin3.li@intel.com>
 <20240207172646.3981-12-xin3.li@intel.com> <Zi9ZSuwQXl8/Ncs/@chao-email>
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> >+/*
> >+ * It's enough to check just CR4.FRED (X86_CR4_FRED) to tell if
> >+ * a vCPU is running with FRED enabled, because:
> >+ * 1) CR4.FRED can be set to 1 only _after_ IA32_EFER.LMA =3D 1.
> >+ * 2) To leave IA-32e mode, CR4.FRED must be cleared first.
> >+ *
> >+ * More details at FRED Spec 6.0 Section 4.2 Enabling in CR4.
> >+ */
>=20
> I think we can give more context here, e.g.,
>=20
> Although FRED architecture applies to 64-bit mode only, there is no need =
to check if
> the CPU is in 64-bit mode (i.e., IA32_EFER.LMA and CS.L) to tell if FRED =
is enabled
> because CR4.FRED=3D1 implies the CPU is in 64-bit mode.

What is "more context" here?

> Specifically,