linux-kernel - Re: [PATCH RFC v1 07/20] KVM: nVMX: Support the extended instruction info field

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Message-ID: <aRvOSnaUt1E+/pkC@intel.com>
Date: Tue, 18 Nov 2025 09:39:22 +0800
From: Chao Gao <chao.gao@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: "Chang S. Bae" <chang.seok.bae@...el.com>, kvm <kvm@...r.kernel.org>,
	"Kernel Mailing List, Linux" <linux-kernel@...r.kernel.org>, "Sean
 Christopherson" <seanjc@...gle.com>, Zhao Liu <zhao1.liu@...el.com>
Subject: Re: [PATCH RFC v1 07/20] KVM: nVMX: Support the extended instruction
 info field

On Tue, Nov 18, 2025 at 12:29:19AM +0100, Paolo Bonzini wrote:
>Il mer 12 nov 2025, 02:54 Chao Gao <chao.gao@...el.com> ha scritto:
>>
>> Shouldn't we check guest's capabilities rather than host's,
>>
>> i.e., guest_cpu_cap_has(X86_FEATURE_APX)?
>
>As the manual says, you're free to use the extended field if
>available, and it's faster.

The point is, from the guest's perspective, the field is available iff the vCPU
supports APX. KVM (L0) doesn't need to virtualize VMCS12's EII field if the vCPU
doesn't have APX.

For other call sites of vmx_egpr_enabled(), I agree we should just check host
capabilities.