linux-kernel - Re: [PATCH 1/2] KVM: x86: Advertise CPUID.(EAX=7,ECX=2):EDX[5:0] to userspace

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Date:   Wed, 25 Oct 2023 15:06:49 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Jim Mattson <jmattson@...gle.com>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        'Paolo Bonzini ' <pbonzini@...hat.com>,
        'Sean Christopherson ' <seanjc@...gle.com>
Subject: Re: [PATCH 1/2] KVM: x86: Advertise CPUID.(EAX=7,ECX=2):EDX[5:0] to
 userspace

On Mon, Oct 23, 2023 at 05:16:35PM -0700, Jim Mattson wrote:
>The low five bits {INTEL_PSFD, IPRED_CTRL, RRSBA_CTRL, DDPD_U, BHI_CTRL}
>advertise the availability of specific bits in IA32_SPEC_CTRL. Since KVM
>dynamically determines the legal IA32_SPEC_CTRL bits for the underlying
>hardware, the hard work has already been done. Just let userspace know
>that a guest can use these IA32_SPEC_CTRL bits.
>
>The sixth bit (MCDT_NO) states that the processor does not exhibit MXCSR
>Configuration Dependent Timing (MCDT) behavior. This is an inherent
>property of the physical processor that is inherited by the virtual
>CPU. Pass that information on to userspace.
>
>Signed-off-by: Jim Mattson <jmattson@...gle.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>