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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id u17sm11835476eje.11.2020.12.07.03.29.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Dec 2020 03:29:35 -0800 (PST) Subject: Re: KVM_SET_CPUID doesn't check supported bits (was Re: [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup) To: stsp , Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20201007014417.29276-1-sean.j.christopherson@intel.com> <99334de1-ba3d-dfac-0730-e637d39b948f@yandex.ru> <20201008175951.GA9267@linux.intel.com> <7efe1398-24c0-139f-29fa-3d89b6013f34@yandex.ru> <20201009040453.GA10744@linux.intel.com> <5dfa55f3-ecdf-9f8d-2d45-d2e6e54f2daa@yandex.ru> <20201009153053.GA16234@linux.intel.com> From: Paolo Bonzini Message-ID: Date: Mon, 7 Dec 2020 12:29:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 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: linux-kernel@vger.kernel.org On 07/12/20 12:24, stsp wrote: > It tries to enable VME among other things. > qemu appears to disable VME by default, > unless you do "-cpu host". So we have a situation where > the host (which is qemu) doesn't have VME, > and guest (dosemu) is trying to enable it. > Now obviously KVM_SET_CPUID doesn't check anyting > at all and returns success. That later turns > into an invalid guest state. > > > Question: should KVM_SET_CPUID check for > supported bits, end return error if not everything > is supported? No, it is intentional. Most bits of CPUID are not ever checked by KVM, so userspace is supposed to set values that makes sense or just copy the value of KVM_GET_SUPPORTED_CPUID more or less blindly. Paolo