linux-kernel - Re: [PATCH v1 8/8] kvm:cpuid Report CET SHSTK and IBT support in CPUID.(EAX=0x7,ECX=0).

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Message-ID: <72bb7ac5-1137-2a4a-de5e-5a3db53a0b13@redhat.com>
Date:   Mon, 7 Jan 2019 17:03:55 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, yi.z.zhang@...el.com, hjl.tools@...il.com
Cc:     Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v1 8/8] kvm:cpuid Report CET SHSTK and IBT support in
 CPUID.(EAX=0x7,ECX=0).

On 26/12/18 09:15, Yang Weijiang wrote:
> Guest OS can query CET SHSTK and IBT support by CPUID.(EAX=0x7,ECX=0),
> in return, ECX[bit 7] corresponds to SHSTK feature, and EDX[bit 20]
> corresponds to IBT feature.
> 
> Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 55c282f71f93..d7b60b3c4326 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -67,6 +67,8 @@ u64 kvm_supported_xcr0(void)
>  
>  #define F(x) bit(X86_FEATURE_##x)
>  
> +#define CET_IBT_BIT bit(20)
> +
>  /* For scattered features from cpufeatures.h; we currently expose none */
>  #define KF(x) bit(KVM_CPUID_BIT_##x)
>  
> @@ -407,12 +409,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  		F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ |
>  		F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
>  		F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
> -		F(CLDEMOTE);
> +		F(CLDEMOTE) | F(SHSTK);
>  
>  	/* 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) | CET_IBT_BIT;
>  
>  	/* all calls to cpuid_count() should be made on the same cpu */
>  	get_cpu();
> 

This might change soon, but at least for now KVM's XSAVES/XRSTORS usage
depends on Linux's.  Therefore, this should only be enabled if Linux has
set bits 11 and 12 in MSR_IA32_XSS.

Paolo