diff options
| -rw-r--r-- | arch/x86/kvm/cpuid.c | 31 |
1 files changed, 21 insertions, 10 deletions
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index cce78723376c..870995d13644 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -408,9 +408,6 @@ static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array, &entry->eax, &entry->ebx, &entry->ecx, &entry->edx); switch (function) { - case 2: - entry->flags |= KVM_CPUID_FLAG_STATEFUL_FUNC; - break; case 4: case 7: case 0xb: @@ -486,17 +483,31 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) * it since we emulate x2apic in software */ cpuid_entry_set(entry, X86_FEATURE_X2APIC); break; - /* function 2 entries are STATEFUL. That is, repeated cpuid commands - * may return different values. This forces us to get_cpu() before - * issuing the first command, and also to emulate this annoying behavior - * in kvm_emulate_cpuid() using KVM_CPUID_FLAG_STATE_READ_NEXT */ case 2: + /* + * On ancient CPUs, function 2 entries are STATEFUL. That is, + * CPUID(function=2, index=0) may return different results each + * time, with the least-significant byte in EAX enumerating the + * number of times software should do CPUID(2, 0). + * + * Modern CPUs (quite likely every CPU KVM has *ever* run on) + * are less idiotic. Intel's SDM states that EAX & 0xff "will + * always return 01H. Software should ignore this value and not + * interpret it as an informational descriptor", while AMD's + * APM states that CPUID(2) is reserved. + */ + max_idx = entry->eax & 0xff; + if (likely(max_idx <= 1)) + break; + + entry->flags |= KVM_CPUID_FLAG_STATEFUL_FUNC; entry->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT; - for (i = 1, max_idx = entry->eax & 0xff; i < max_idx; ++i) { + for (i = 1; i < max_idx; ++i) { entry = do_host_cpuid(array, function, 0); if (!entry) goto out; + entry->flags |= KVM_CPUID_FLAG_STATEFUL_FUNC; } break; /* functions 4 and 0x8000001d have additional index. */ @@ -909,7 +920,7 @@ static int is_matching_cpuid_entry(struct kvm_cpuid_entry2 *e, return 0; if ((e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX) && e->index != index) return 0; - if ((e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC) && + if (unlikely(e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC) && !(e->flags & KVM_CPUID_FLAG_STATE_READ_NEXT)) return 0; return 1; @@ -926,7 +937,7 @@ struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu, e = &vcpu->arch.cpuid_entries[i]; if (is_matching_cpuid_entry(e, function, index)) { - if (e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC) + if (unlikely(e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC)) move_to_next_stateful_cpuid_entry(vcpu, i); best = e; break; |