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

Paolo Bonzini
2019-03-04T08:38:58Z

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

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