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

[Xiaoyao Li <xiaoyao.li@linux.intel.com>]

On Mon, 2019-03-04 at 11:49 +0100, Paolo Bonzini wrote:
> On 04/03/19 11:47, Xiaoyao Li wrote:
> > 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);
> > 		}
> > 		...
> > 	...
> > 	}
> > ...
> > }
> 
> Yes, exactly.
> 
> Paolo

Like you said before, I think we don't need the condition judgment
"if(boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))", but to set F(CORE_CAPABILITY)
always for guest since MSR_IA32_CORE_CAPABILITY is emulated.

And we should set the right emulated value of MSR_IA32_CORE_CAPABILITY for guest
in function kvm_get_core_capability() based on whether
boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT) just as you commented in the next
patch.

Xiaoyao

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