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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id n62sm4120086wmb.10.2020.10.22.07.44.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Oct 2020 07:44:54 -0700 (PDT) Subject: Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED_CPUID To: Xiaoyao Li , Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1603330475-7063-1-git-send-email-wanpengli@tencent.com> <6ad94df6-9ecd-e364-296a-34ba41e938b1@intel.com> <31b189e0-503f-157d-7af0-329744ed5369@redhat.com> <18e7a0c6-faff-8c4c-0830-a0bc02627a36@intel.com> From: Paolo Bonzini Message-ID: <4a5d0ccd-f6a7-2afe-2480-991ff7e079b4@redhat.com> Date: Thu, 22 Oct 2020 16:44:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <18e7a0c6-faff-8c4c-0830-a0bc02627a36@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 22/10/20 16:28, Xiaoyao Li wrote: > On 10/22/2020 10:06 PM, Paolo Bonzini wrote: >> On 22/10/20 15:31, Xiaoyao Li wrote: >>>> >>>> It's common for userspace to copy all supported CPUID bits to >>>> KVM_SET_CPUID2, I don't think this is the right behavior for >>>> KVM_HINTS_REALTIME. >>> >>> It reminds of X86_FEATURE_WAITPKG, which is added to supported CPUID >>> recently as a fix but QEMU exposes it to guest only when "-overcommit >>> cpu-pm" >> >> WAITPKG is not included in KVM_GET_SUPPORTED_CPUID either.  QEMU detects >> it through the MSR_IA32_UMWAIT register. > > Doesn't 0abcc8f65cc2 ("KVM: VMX: enable X86_FEATURE_WAITPKG in KVM > capabilities") add WAITPKG to KVM_GET_SUPPORTED_CPUID? You're right, I shouldn't have checked only cpuid.c. :) Still I think WAITPKG is different, because it's only for userspace and it's always possible for userspace to do "for(;;)" and burn CPU. KVM_HINTS_REALTIME is more similar to MONITOR, which is not set. Paolo