linux-kernel - Re: [PATCH v4 15/17] kvm: x86: Report CORE_CAPABILITY on GET_SUPPORTED

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Date:   Mon, 4 Mar 2019 09:38:58 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        kvm@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...ux.intel.com>
Subject: Re: [PATCH v4 15/17] kvm: x86: Report CORE_CAPABILITY on
 GET_SUPPORTED_CPUID

On 02/03/19 03:45, Fenghua Yu wrote:
> From: Xiaoyao Li <xiaoyao.li@...ux.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@...ux.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();
>