Re: [PATCH v3 3/8] KVM:CPUID: Add CPUID support for Guest CET

[Sean Christopherson]

On Mon, Feb 25, 2019 at 09:27:11PM +0800, Yang Weijiang wrote:
> Guest CET SHSTK and IBT capability are reported via
> CPUID.(EAX=7, ECX=0):ECX[bit 7] and EDX[bit 20] respectively.
> Guest user mode and supervisor mode xsaves component size
> is reported via CPUID.(EAX=0xD, ECX=1):ECX[bit 11] and ECX[bit 12]
> respectively.
> 
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
>  arch/x86/kvm/cpuid.c | 60 +++++++++++++++++++++++++++++++++-----------
>  arch/x86/kvm/x86.h   |  4 +++
>  2 files changed, 50 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index cb1aece25b17..5e05756cc6db 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -65,6 +65,16 @@ u64 kvm_supported_xcr0(void)
>  	return xcr0;
>  }
>  
> +u64 kvm_supported_xss(void)
> +{
> +	u64 xss;
> +
> +	rdmsrl(MSR_IA32_XSS, xss);
> +	xss &= KVM_SUPPORTED_XSS;
> +	return xss;
> +}
> +EXPORT_SYMBOL(kvm_supported_xss);
> +
>  #define F(x) bit(X86_FEATURE_##x)
>  
>  /* For scattered features from cpufeatures.h; we currently expose none */
> @@ -323,6 +333,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  				 u32 index, int *nent, int maxnent)
>  {
>  	int r;
> +	u32 eax, ebx, ecx, edx;
>  	unsigned f_nx = is_efer_nx() ? F(NX) : 0;
>  #ifdef CONFIG_X86_64
>  	unsigned f_gbpages = (kvm_x86_ops->get_lpage_level() == PT_PDPE_LEVEL)
> @@ -503,6 +514,20 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			 * if the host doesn't support it.
>  			 */
>  			entry->edx |= F(ARCH_CAPABILITIES);
> +
> +			/*
> +			 * Guest OS CET enabling is designed independent to
> +			 * host enabling, it only has dependency on Host HW
> +			 * capability, if it has, report CET support to
> +			 * Guest.
> +			 */
> +			cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
> +			if (ecx & F(SHSTK))
> +				entry->ecx |= F(SHSTK);
> +
> +			if (edx & F(IBT))
> +				entry->edx |= F(IBT);

There's no need to manually add these flags.  They will be automatically
kept if supported in hardware because your previous patch, 02/08, added
them to the mask of features that can be exposed to the guest,
i.e. set them in kvm_cpuid_7_0_e{c,d}x_x86_features.

> +
>  		} else {
>  			entry->ebx = 0;
>  			entry->ecx = 0;
> @@ -564,14 +589,17 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  	}
>  	case 0xd: {
>  		int idx, i;
> -		u64 supported = kvm_supported_xcr0();
> +		u64 u_supported = kvm_supported_xcr0();
> +		u64 s_supported = kvm_supported_xss();
> +		u64 supported;
> +		int compacted;
>  
> -		entry->eax &= supported;
> -		entry->ebx = xstate_required_size(supported, false);
> +		entry->eax &= u_supported;
> +		entry->ebx = xstate_required_size(u_supported, false);
>  		entry->ecx = entry->ebx;
> -		entry->edx &= supported >> 32;
> +		entry->edx &= u_supported >> 32;
>  		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
> -		if (!supported)
> +		if (!u_supported && !s_supported)
>  			break;
>  
>  		for (idx = 1, i = 1; idx < 64; ++idx) {
> @@ -583,19 +611,23 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			if (idx == 1) {
>  				entry[i].eax &= kvm_cpuid_D_1_eax_x86_features;
>  				cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
> -				entry[i].ebx = 0;
> -				if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
> -					entry[i].ebx =
> -						xstate_required_size(supported,
> -								     true);
> +				supported = u_supported | s_supported;
> +				compacted = entry[i].eax &
> +					(F(XSAVES) | F(XSAVEC));
> +				entry[i].ebx = xstate_required_size(supported,
> +								    compacted);
> +				entry[i].ecx &= s_supported;
> +				entry[i].edx = 0;
>  			} else {
> +				supported = (entry[i].ecx & 1) ? s_supported :
> +								 u_supported;
>  				if (entry[i].eax == 0 || !(supported & mask))
>  					continue;
> -				if (WARN_ON_ONCE(entry[i].ecx & 1))
> -					continue;
> +				entry[i].ecx &= 1;
> +				entry[i].edx = 0;
> +				if (entry[i].ecx)
> +					entry[i].ebx = 0;
>  			}
> -			entry[i].ecx = 0;
> -			entry[i].edx = 0;
>  			entry[i].flags |=
>  			       KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
>  			++*nent;
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 224cd0a47568..c61da41c3c5c 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -283,6 +283,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, unsigned long cr2,
>  				| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
>  				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>  				| XFEATURE_MASK_PKRU)
> +
> +#define KVM_SUPPORTED_XSS	(XFEATURE_MASK_SHSTK_USER \
> +				| XFEATURE_MASK_SHSTK_KERNEL)
> +
>  extern u64 host_xcr0;
>  
>  extern u64 kvm_supported_xcr0(void);
> -- 
> 2.17.1
>