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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.googlemail.com with ESMTPSA id z5sm3005850wmp.10.2022.01.18.04.52.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Jan 2022 04:53:00 -0800 (PST) Message-ID: <29573e51-aa21-dbf3-b626-facf72e5b9c6@redhat.com> Date: Tue, 18 Jan 2022 13:52:56 +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: [RFC PATCH 3/7] x86: Grant AMX permission for guest Content-Language: en-US To: Yang Zhong , qemu-devel@nongnu.org References: <20220107093134.136441-1-yang.zhong@intel.com> <20220107093134.136441-4-yang.zhong@intel.com> From: Paolo Bonzini In-Reply-To: <20220107093134.136441-4-yang.zhong@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Host-Lookup-Failed: Reverse DNS lookup failed for 2a00:1450:4864:20::32a (failed) Received-SPF: pass client-ip=2a00:1450:4864:20::32a; envelope-from=paolo.bonzini@gmail.com; helo=mail-wm1-x32a.google.com X-Spam_score_int: -6 X-Spam_score: -0.7 X-Spam_bar: / X-Spam_report: (-0.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.248, NICE_REPLY_A=-0.001, PDS_HP_HELO_NORDNS=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: seanjc@google.com, kevin.tian@intel.com, jing2.liu@linux.intel.com, wei.w.wang@intel.com, guang.zeng@intel.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 1/7/22 10:31, Yang Zhong wrote: > +static void x86_xsave_req_perm(void) > +{ > + unsigned long bitmask; > + > + long rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, > + XSTATE_XTILE_DATA_BIT); > + if (rc) { > + /* > + * The older kernel version(<5.15) can't support > + * ARCH_REQ_XCOMP_GUEST_PERM and directly return. > + */ > + return; > + } > + > + rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, &bitmask); > + if (rc) { > + error_report("prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld", rc); > + } else if (!(bitmask & XFEATURE_XTILE_MASK)) { > + error_report("prctl(ARCH_REQ_XCOMP_GUEST_PERM) failure " > + "and bitmask=0x%lx", bitmask); > + exit(EXIT_FAILURE); > + } > +} > + > void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version) > { > int i; > @@ -124,6 +150,8 @@ void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version) > MachineState *ms = MACHINE(x86ms); > MachineClass *mc = MACHINE_GET_CLASS(x86ms); > > + /* Request AMX pemission for guest */ > + x86_xsave_req_perm(); > x86_cpu_set_default_version(default_cpu_version); > This should be done before creating a CPU with support for state component 18. It happens in kvm_init_vcpu, with the following call stack: kvm_init_vcpu kvm_vcpu_thread_fn kvm_start_vcpu_thread qemu_init_vcpu x86_cpu_realizefn The issue however is that this has to be done before KVM_GET_SUPPORTED_CPUID and KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2). For the former, you can assume that anything returned by ARCH_GET_XCOMP_GUEST_PERM will be returned by KVM_GET_SUPPORTED_CPUID in CPUID[0xD].EDX:EAX, so you can: - add it to kvm_arch_get_supported_cpuid