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

[Paolo Bonzini]

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@xxxxxxxxxxxxxxx>
>>>
>>> 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@xxxxxxxxxxxxxxx>
>>> ---
>>>  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

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