Re: [RFC PATCH v4 2/8] KVM:CPUID: Add CET CPUID support for Guest

[Sean Christopherson]

On Mon, Mar 18, 2019 at 11:03:45PM +0800, Yang Weijiang wrote:
> CET SHSTK and IBT capability are reported via
> CPUID.(EAX=7, ECX=0):ECX[bit 7] and EDX[bit 20] respectively.
> CR4.CET[bit 23] is CET master enable bit, it controls CET feature
> enabling. CET user mode and supervisor mode xsaves component size
> is reported via CPUID.(EAX=0xD, ECX=1):ECX[bit 11] and ECX[bit 12]
> respectively.
> 
> Note: Although SHSTK or IBT can be enabled independently,
>       both of them are controlled by CR4.CET.
> 
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |  4 +++-
>  arch/x86/kvm/cpuid.c            | 41 ++++++++++++++++++++++-----------
>  arch/x86/kvm/vmx.c              |  6 +++++
>  arch/x86/kvm/x86.h              |  4 ++++
>  4 files changed, 40 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 55e51ff7e421..fc038bf1924a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -90,7 +90,8 @@
>  			  | X86_CR4_PGE | X86_CR4_PCE | X86_CR4_OSFXSR | X86_CR4_PCIDE \
>  			  | X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
>  			  | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_VMXE \
> -			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP))
> +			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP \
> +			  | X86_CR4_CET))
>  
>  #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
>  
> @@ -1185,6 +1186,7 @@ struct kvm_x86_ops {
>  
>  	int (*nested_enable_evmcs)(struct kvm_vcpu *vcpu,
>  				   uint16_t *vmcs_version);
> +	u64 (*vmx_supported_xss)(void);
>  };
>  
>  struct kvm_arch_async_pf {
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 7bcfa61375c0..53abd6019c68 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -65,6 +65,11 @@ u64 kvm_supported_xcr0(void)
>  	return xcr0;
>  }
>  
> +u64 kvm_supported_xss(void)
> +{
> +	return KVM_SUPPORTED_XSS & kvm_x86_ops->vmx_supported_xss();
> +}
> +
>  #define F(x) bit(X86_FEATURE_##x)
>  
>  /* For scattered features from cpufeatures.h; we currently expose none */
> @@ -406,12 +411,12 @@ 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) | F(IBT);

The features should not be advertised to userspace until KVM fully supports
them, which AIUI doesn't happen until the last patch in this series.

>  
>  	/* all calls to cpuid_count() should be made on the same cpu */
>  	get_cpu();
> @@ -564,14 +569,16 @@ 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;
>  
> -		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 +590,25 @@ 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);
> +				supported = u_supported | s_supported;
>  				entry[i].ebx = 0;
> -				if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
> +				entry[i].edx = 0;
> +				entry[i].ecx &= s_supported;
> +				if (entry[i].eax & (F(XSAVES) | F(XSAVEC))) {
>  					entry[i].ebx =
> -						xstate_required_size(supported,
> -								     true);
> +					xstate_required_size(supported,
> +							     true);

The indentation depth is getting pretty gnarly, I at a glance I think it'd
be much cleaner to move the guts of the for loop to a helper, e.g.:

		for (idx = 1, i = 1; idx < 64; ++idx, ++i) {
			if (*nent >= maxnent)
				goto out;

			__do_cpuid_0xd_ent(i, u_supported, s_supported);

			++*nent;
		}
> +				}
>  			} 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;

Not your code, but the "++i;" that's sitting below this should be handled
in the for loop (see above).  This is a good opportunity to make that change.

> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 7bbb8b26e901..53cef5a3db96 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4169,6 +4169,11 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	return 0;
>  }
>  
> +static __always_inline u64 vmx_supported_xss(void)
> +{
> +	return host_xss;
> +}
> +
>  static void vmx_leave_nested(struct kvm_vcpu *vcpu);
>  
>  /*
> @@ -15107,6 +15112,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
>  	.enable_smi_window = enable_smi_window,
>  
>  	.nested_enable_evmcs = nested_enable_evmcs,
> +	.vmx_supported_xss = vmx_supported_xss,
>  };
>  
>  static void vmx_cleanup_l1d_flush(void)
> 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
>