On Thu, Jul 16, 2009 at 02:09:09PM +0800, Sheng Yang wrote: > On Thursday 16 July 2009 14:00:15 Gleb Natapov wrote: > > On Thu, Jul 16, 2009 at 09:46:21AM +0800, Sheng Yang wrote: > > > On Thursday 16 July 2009 07:01:30 Marcelo Tosatti wrote: > > > > On Sun, Jul 12, 2009 at 04:10:55PM +0300, Gleb Natapov wrote: > > > > > We emulate x2apic in software, so host support is not required. > > > > > > > > > > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx> > > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > > > index 00844eb..c256da7 100644 > > > > > --- a/arch/x86/kvm/x86.c > > > > > +++ b/arch/x86/kvm/x86.c > > > > > @@ -1497,6 +1497,9 @@ static void do_cpuid_ent(struct > > > > > kvm_cpuid_entry2 *entry, u32 function, case 1: > > > > > entry->edx &= kvm_supported_word0_x86_features; > > > > > entry->ecx &= kvm_supported_word4_x86_features; > > > > > + /* we support x2apic emulation even if host does not support > > > > > + it since we emulate x2apic in software */ > > > > > + entry->ecx |= F(X2APIC); > > > > > break; > > > > > /* function 2 entries are STATEFUL. That is, repeated cpuid > > > > > commands * may return different values. This forces us to get_cpu() > > > > > before -- > > > > > Gleb. > > > > > > > > What if you have an older host that does not support emulate x2apic? > > > > > > Due to interrupt remapping can't be enabled with KVM now, I think older > > > host would just ignore this info... (The new one can work without > > > interrupt remapping with KVM). > > > > > > By the way, I saw X2APIC in host supported CPUID feature list(1.ecx), > > > which I > > > > Where have you seen it? If you mean kvm_supported_word4_x86_features > > then it is not what is supported by the host, but what is supported by > > KVM. Host unsupported bits are dropped from there before reporting to > > userspace. That is why this patch what necessary. > > Yes, that's what I mean. x2apic feature needn't judged by host feature, we can > always set the bit to support it, no need for a filter. I think put it in the > kvm_supported_word4_x86_features is a little misleading means that KVM support > it through host feature rather than emulation. > Yeah, I put it there initially since I misunderstood how things work and thought that it will be reported to userspace (and usercpace had a bug that prevented me from discovering the problem). -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
