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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id oz31sm671867ejc.35.2022.01.13.01.27.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Jan 2022 01:27:31 -0800 (PST) From: Vitaly Kuznetsov To: Paolo Bonzini , Igor Mammedov Cc: kvm@vger.kernel.org, Sean Christopherson , Wanpeng Li , Jim Mattson , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN In-Reply-To: <50136685-706e-fc6a-0a77-97e584e74f93@redhat.com> References: <20211122175818.608220-1-vkuznets@redhat.com> <20211122175818.608220-3-vkuznets@redhat.com> <16368a89-99ea-e52c-47b6-bd006933ec1f@redhat.com> <20211227183253.45a03ca2@redhat.com> <61325b2b-dc93-5db2-2d0a-dd0900d947f2@redhat.com> <87mtkdqm7m.fsf@redhat.com> <20220103104057.4dcf7948@redhat.com> <875yr1q8oa.fsf@redhat.com> <87o84qpk7d.fsf@redhat.com> <877dbbq5om.fsf@redhat.com> <5505d731-cf87-9662-33f3-08844d92877c@redhat.com> <20220111090022.1125ffb5@redhat.com> <87fsptnjic.fsf@redhat.com> <50136685-706e-fc6a-0a77-97e584e74f93@redhat.com> Date: Thu, 13 Jan 2022 10:27:30 +0100 Message-ID: <87bl0gnfy5.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 1/12/22 14:58, Vitaly Kuznetsov wrote: >> - best = kvm_find_cpuid_entry(vcpu, 0xD, 1); >> + best = cpuid_entry2_find(entries, nent, 0xD, 1); >> if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) || >> cpuid_entry_has(best, X86_FEATURE_XSAVEC))) >> best->ebx = xstate_required_size(vcpu->arch.xcr0, true); >> >> - best = kvm_find_kvm_cpuid_features(vcpu); >> + best = __kvm_find_kvm_cpuid_features(vcpu, vcpu->arch.cpuid_entries, >> + vcpu->arch.cpuid_nent); >> if (kvm_hlt_in_guest(vcpu->kvm) && best && > > I think this should be __kvm_find_kvm_cpuid_features(vcpu, entries, nent). > Of course. >> >> + case 0x1: >> + /* Only initial LAPIC id is allowed to change */ >> + if (e->eax ^ best->eax || ((e->ebx ^ best->ebx) >> 24) || >> + e->ecx ^ best->ecx || e->edx ^ best->edx) >> + return -EINVAL; >> + break; > > This XOR is a bit weird. In addition the EBX test is checking the wrong > bits (it checks whether 31:24 change and ignores changes to 23:0). Indeed, however, I've tested CPU hotplug with QEMU trying different CPUs in random order and surprisingly othing blew up, feels like QEMU was smart enough to re-use the right fd) > > You can write just "(e->ebx & ~0xff000000u) != (best->ebx ~0xff000000u)". > >> >> + default: >> + if (e->eax ^ best->eax || e->ebx ^ best->ebx || >> + e->ecx ^ best->ecx || e->edx ^ best->edx) >> + return -EINVAL; > > This one even more so. Thanks for the early review, I'm going to prepare a selftest and send this out. -- Vitaly