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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.googlemail.com with ESMTPSA id w7sm13761219wrv.96.2022.01.17.09.31.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Jan 2022 09:31:59 -0800 (PST) Message-ID: <301d4800-5eab-6e21-e8c1-2f87789fc4b9@redhat.com> Date: Mon, 17 Jan 2022 18:31:58 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing Content-Language: en-US To: Like Xu Cc: Jing Liu , Sean Christopherson , Jim Mattson , Vitaly Kuznetsov , Wanpeng Li , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20220117074531.76925-1-likexu@tencent.com> From: Paolo Bonzini In-Reply-To: <20220117074531.76925-1-likexu@tencent.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/17/22 08:45, Like Xu wrote: > From: Like Xu > > 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 > --- > 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