From: Paolo Bonzini <pbonzini@redhat.com>
To: Like Xu <like.xu.linux@gmail.com>
Cc: Jing Liu <jing2.liu@intel.com>,
Sean Christopherson <seanjc@google.com>,
Jim Mattson <jmattson@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing
Date: Mon, 17 Jan 2022 18:31:58 +0100 [thread overview]
Message-ID: <301d4800-5eab-6e21-e8c1-2f87789fc4b9@redhat.com> (raw)
In-Reply-To: <20220117074531.76925-1-likexu@tencent.com>
On 1/17/22 08:45, Like Xu wrote:
> From: Like Xu <likexu@tencent.com>
>
> According to Intel extended feature disable (XFD) spec, the sub-function i
> (i > 1) of CPUID function 0DH enumerates "details for state component i.
> ECX[2] enumerates support for XFD support for this state component."
>
> If KVM does not report F(XFD) feature (e.g. due to CONFIG_X86_64),
> then the corresponding XFD support for any state component i
> should also be removed. Translate this dependency into KVM terms.
>
> Fixes: 690a757d610e ("kvm: x86: Add CPUID support for Intel AMX")
> Signed-off-by: Like Xu <likexu@tencent.com>
> ---
> arch/x86/kvm/cpuid.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c55e57b30e81..e96efef4f048 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -886,6 +886,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> --array->nent;
> continue;
> }
> +
> + if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
> + entry->ecx &= ~BIT_ULL(2);
> entry->edx = 0;
> }
> break;
Generally this is something that is left to userspace. Apart from the
usecase of "call KVM_GET_SUPPORTED_CPUID and pass it to KVM_SET_CPUID2",
userspace should know what any changed bits mean.
Paolo
next prev parent reply other threads:[~2022-01-17 17:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-17 7:45 [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing Like Xu
2022-01-17 17:31 ` Paolo Bonzini [this message]
2022-01-18 6:43 ` Like Xu
2022-01-18 8:42 ` Paolo Bonzini
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