linux-kernel - Re: [PATCH] kvm: x86: Report STIBP on GET_SUPPORTED

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Date:   Wed, 5 Dec 2018 17:02:06 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Eduardo Habkost <ehabkost@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        KarimAllah Ahmed <karahmed@...zon.de>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] kvm: x86: Report STIBP on GET_SUPPORTED_CPUID

On Wed, Dec 05, 2018 at 05:19:56PM -0200, Eduardo Habkost wrote:
> Months ago, we have added code to allow direct access to MSR_IA32_SPEC_CTRL
> to the guest, which makes STIBP available to guests.  This was implemented
> by commits d28b387fb74d ("KVM/VMX: Allow direct access to
> MSR_IA32_SPEC_CTRL") and b2ac58f90540 ("KVM/SVM: Allow direct access to
> MSR_IA32_SPEC_CTRL").
> 
> However, we never updated GET_SUPPORTED_CPUID to let userspace know that
> STIBP can be enabled in CPUID.  Fix that by updating

Ooops!
> kvm_cpuid_8000_0008_ebx_x86_features and kvm_cpuid_7_0_edx_x86_features.

Shouldn't there also be a patch in QEMU to use it? (aka, +stibp).

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

Thank you!
> Signed-off-by: Eduardo Habkost <ehabkost@...hat.com>
> ---
>  arch/x86/kvm/cpuid.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 7bcfa61375c0..cc6dd65828a4 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -381,7 +381,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  	/* cpuid 0x80000008.ebx */
>  	const u32 kvm_cpuid_8000_0008_ebx_x86_features =
>  		F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) |
> -		F(AMD_SSB_NO);
> +		F(AMD_SSB_NO) | F(AMD_STIBP);
>  
>  	/* cpuid 0xC0000001.edx */
>  	const u32 kvm_cpuid_C000_0001_edx_x86_features =
> @@ -411,7 +411,7 @@ 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(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP);
>  
>  	/* all calls to cpuid_count() should be made on the same cpu */
>  	get_cpu();
> -- 
> 2.18.0.rc1.1.g3f1ff2140
>