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

Paolo Bonzini
2019-03-04T10:49:11Z

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

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