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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id p4sm2499967ejr.81.2021.05.05.01.01.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 May 2021 01:01:55 -0700 (PDT) Subject: Re: [PATCH 02/15] KVM: x86: Emulate RDPID only if RDTSCP is supported To: Reiji Watanabe , Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Xiaoyao Li References: <20210504171734.1434054-1-seanjc@google.com> <20210504171734.1434054-3-seanjc@google.com> From: Paolo Bonzini Message-ID: <92131802-68b7-3d27-3e61-9b388bfcbc7f@redhat.com> Date: Wed, 5 May 2021 10:01:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 05/05/21 05:51, Reiji Watanabe wrote: >> --- a/arch/x86/kvm/cpuid.c >> +++ b/arch/x86/kvm/cpuid.c >> @@ -637,7 +637,8 @@ static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func) >> case 7: >> entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX; >> entry->eax = 0; >> - entry->ecx = F(RDPID); >> + if (kvm_cpu_cap_has(X86_FEATURE_RDTSCP)) >> + entry->ecx = F(RDPID); >> ++array->nent; >> default: >> break; > I'm wondering if entry->ecx should be set to F(RDPID) here > even if the CPU supports RDPID natively. > (i.e. kvm_cpu_cap_has(X86_FEATURE_RDPID) is true) > > The document "Documentation/virt/kvm/api.rst" says: > --- > 4.88 KVM_GET_EMULATED_CPUID > --------------------------- > <...> > Userspace can use the information returned by this ioctl to query > which features are emulated by kvm instead of being present natively. > --- Setting it always is consistent with the treatment of MOVBE above. Either way is okay but it should be done for both bits. Paolo