On 11/04/2016 22:54, Radim Krčmář wrote:
>> >
>> > static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2
>> > *entry)
>> > {
>> > switch (func) {
>> > + case 0x00000001:
> ("case 1:" or "case 0x1:" would be easier to read.)
>
>> > + if (avic)
>> > + entry->ecx &= ~bit(X86_FEATURE_X2APIC);
>> > + break;
>
> ---
> A rant for the unlikely case I get back to fix the broader situation:
> Only one of these two additions is needed. If we do the second one,
> then userspace should not set X2APIC, therefore the first one is
> useless.
>
> Omitting the second one allows userspace to clear apicv_active and set
> X86_FEATURE_X2APIC, but it needs a non-intuitive order of ioctls, so I
> think we should have the second one.
>
> The problem is that KVM doesn't seems to check whether userspace sets
> cpuid that is a subset of supported ones, so omitting the first one
> needlessly expands the space for potential failures.
Yes, we need both.
Paolo
