Re: [PATCH v4 15/17] kvm: x86: Report CORE_CAPABILITY on GET_SUPPORTED_CPUID

Xiaoyao Li
2019-03-04T10:47:19Z

On Mon, 2019-03-04 at 09:38 +0100, Paolo Bonzini wrote:
> On 02/03/19 03:45, Fenghua Yu wrote:
> > From: Xiaoyao Li <xiaoyao.li@linux.intel.com>
> >
> > In the latest Intel SDM, CPUID.(EAX=7H,ECX=0):EDX[30] will enumerate
> > the presence of the IA32_CORE_CAPABILITY MSR.
> >
> > Update GET_SUPPORTED_CPUID to expose this feature bit to user space, so
> > that user space know this bit can be enabled in CPUID.
> >
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@linux.intel.com>
> > ---
> > arch/x86/kvm/cpuid.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index c07958b59f50..e0e17b9c65da 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -410,7 +410,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2
> > *entry, u32 function,
> > /* cpuid 7.0.edx*/
> > const u32 kvm_cpuid_7_0_edx_x86_features =
> > F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
> > - F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP);
> > + F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(CORE_CAPABILITY) |
> > + F(INTEL_STIBP);
>
> This should be enabled always if boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT),
> since the MSR is emulated. This way, guests can always rely on
> IA32_CORE_CAPABILITY_MSR and it won't have to rely on the FMS
> (which means nothing inside a guest).
>
> Paolo

Hi, Paolo
Do you mean that we don't need this here, but to add the handling below?

static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 * entry, u32 function,
...
switch (function) {
...
case 7: {
...
if (index ==0) {
...
if(boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
entry->edx |= F(CORE_CAPABILITY);
}
...
...
}
...
}

> > /* all calls to cpuid_count() should be made on the same cpu */
> > get_cpu();
> >
>
>