linux-kernel - RE: [PATCH v1 11/23] KVM: x86: Add kvm_is_fred

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Date:   Tue, 14 Nov 2023 04:42:13 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     "Gao, Chao" <chao.gao@...el.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
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        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
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        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "Cui, Dexuan" <decui@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "peterz@...radead.org" <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v1 11/23] KVM: x86: Add kvm_is_fred_enabled()

> >+	return cpu_feature_enabled(X86_FEATURE_FRED) &&
> >+	       kvm_is_cr4_bit_set(vcpu, X86_CR4_FRED);
> 
> FRED is enabled when CR4.FRED = IA32_EFER.LMA = 1. Any reason to omit the
> check about long mode?

It won' t allow CR4.FRED to be set if not in long mode, I don't expect it
at runtime.  Or you have one?

If you are talking about save/restore a corrupted vCPU state, a following
VM entry should fail anyway.