On Thu, 2022-01-13 at 10:27 +0100, Vitaly Kuznetsov wrote: > Paolo Bonzini <pbonzini@xxxxxxxxxx> 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. > I also looked at this recently (due to other reasons) and I found out that qemu picks a parked vcpu by its vcpu_id which is its initial apic id, thus apic id related features should not change. Take a look at 'kvm_get_vcpu' in qemu source. Maybe old qemu versions didn't do this? Best regards, Thanks, Maxim Levitsky
