Re: [PATCH v7 24/26] KVM: x86: Enable CET virtualization for VMX and advertise to userspace

["Yang, Weijiang" <weijiang.yang@intel.com>]

On 12/1/2023 1:46 AM, Maxim Levitsky wrote:

[...]

>>   
>> +static inline bool cpu_has_vmx_basic_no_hw_errcode(void)
>> +{
>> +	return	((u64)vmcs_config.basic_cap << 32) &
>> +		 VMX_BASIC_NO_HW_ERROR_CODE_CC;
>> +}
> I still think that we should add a comment explaining why this check is needed,
> as I said in the previous review.

OK, I'll add some comments above the function. Thanks!

>> +
>>   static inline bool cpu_has_virtual_nmis(void)
>>   {
>>   	return vmcs_config.pin_based_exec_ctrl & PIN_BASED_VIRTUAL_NMIS &&
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index c658f2f230df..a1aae8709939 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -2614,6 +2614,7 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>>   		{ VM_ENTRY_LOAD_IA32_EFER,		VM_EXIT_LOAD_IA32_EFER },
>>   		{ VM_ENTRY_LOAD_BNDCFGS,		VM_EXIT_CLEAR_BNDCFGS },
>>   		{ VM_ENTRY_LOAD_IA32_RTIT_CTL,		VM_EXIT_CLEAR_IA32_RTIT_CTL },
>> +		{ VM_ENTRY_LOAD_CET_STATE,		VM_EXIT_LOAD_CET_STATE },
>>   	};
>>   
>>   	memset(vmcs_conf, 0, sizeof(*vmcs_conf));
>> @@ -4935,6 +4936,15 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>   
>>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);  /* 22.2.1 */
>>   
>> +	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK))
>> +		vmcs_writel(GUEST_SSP, 0);
>> +	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK) ||
>> +	    kvm_cpu_cap_has(X86_FEATURE_IBT))
>> +		vmcs_writel(GUEST_S_CET, 0);
>> +	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
>> +	    IS_ENABLED(CONFIG_X86_64))
>> +		vmcs_writel(GUEST_INTR_SSP_TABLE, 0);
> Looks reasonable now.
>> +
>>   	kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
>>   
>>   	vpid_sync_context(vmx->vpid);
>> @@ -6354,6 +6364,12 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
>>   	if (vmcs_read32(VM_EXIT_MSR_STORE_COUNT) > 0)
>>   		vmx_dump_msrs("guest autostore", &vmx->msr_autostore.guest);
>>   
>> +	if (vmentry_ctl & VM_ENTRY_LOAD_CET_STATE) {
>> +		pr_err("S_CET = 0x%016lx\n", vmcs_readl(GUEST_S_CET));
>> +		pr_err("SSP = 0x%016lx\n", vmcs_readl(GUEST_SSP));
>> +		pr_err("INTR SSP TABLE = 0x%016lx\n",
>> +		       vmcs_readl(GUEST_INTR_SSP_TABLE));
>> +	}
>>   	pr_err("*** Host State ***\n");
>>   	pr_err("RIP = 0x%016lx  RSP = 0x%016lx\n",
>>   	       vmcs_readl(HOST_RIP), vmcs_readl(HOST_RSP));
>> @@ -6431,6 +6447,12 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
>>   	if (secondary_exec_control & SECONDARY_EXEC_ENABLE_VPID)
>>   		pr_err("Virtual processor ID = 0x%04x\n",
>>   		       vmcs_read16(VIRTUAL_PROCESSOR_ID));
>> +	if (vmexit_ctl & VM_EXIT_LOAD_CET_STATE) {
>> +		pr_err("S_CET = 0x%016lx\n", vmcs_readl(HOST_S_CET));
>> +		pr_err("SSP = 0x%016lx\n", vmcs_readl(HOST_SSP));
>> +		pr_err("INTR SSP TABLE = 0x%016lx\n",
>> +		       vmcs_readl(HOST_INTR_SSP_TABLE));
>> +	}
>>   }
>>   
>>   /*
>> @@ -7964,7 +7986,6 @@ static __init void vmx_set_cpu_caps(void)
>>   		kvm_cpu_cap_set(X86_FEATURE_UMIP);
>>   
>>   	/* CPUID 0xD.1 */
>> -	kvm_caps.supported_xss = 0;
>>   	if (!cpu_has_vmx_xsaves())
>>   		kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>>   
>> @@ -7976,6 +7997,12 @@ static __init void vmx_set_cpu_caps(void)
>>   
>>   	if (cpu_has_vmx_waitpkg())
>>   		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
>> +
>> +	if (!cpu_has_load_cet_ctrl() || !enable_unrestricted_guest ||
>> +	    !cpu_has_vmx_basic_no_hw_errcode()) {
>> +		kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
>> +		kvm_cpu_cap_clear(X86_FEATURE_IBT);
>> +	}
> My review feedback from previous version still applies here, I don't have an
> idea why this was not addressed....
>
> "I think that here we also need to clear kvm_caps.supported_xss,
> or even better, lets set the CET bits in kvm_caps.supported_xss only
> once CET is fully enabled (both this check and check in __kvm_x86_vendor_init pass)."

Ah, previously I had a helper to check whether CET bits were enabled in kvm_caps.supported_xss,
so need to set the bits earlier before vmx's hardware_setup.  I still want to keep the code as-is
in case other features need to check the their related bits set before configure something in
vmx hardware_setup.

> In addition to that I just checked and unless I am mistaken:
>
> vmx_set_cpu_caps() is called from vmx's hardware_setup(), which is called
> from __kvm_x86_vendor_init.
>
> After this call, __kvm_x86_vendor_init does clear kvm_caps.supported_xss,
> but doesn't do this if the above code cleared X86_FEATURE_SHSTK/X86_FEATURE_IBT.
>
Yeah, I checked the history, the similar logic was there until v6, I can pick it up, thanks!

>>   }
>>   
>>   static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
>> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
>> index c2130d2c8e24..fb72819fbb41 100644
>> --- a/arch/x86/kvm/vmx/vmx.h
>> +++ b/arch/x86/kvm/vmx/vmx.h
>> @@ -480,7 +480,8 @@ static inline u8 vmx_get_rvi(void)
>>   	 VM_ENTRY_LOAD_IA32_EFER |					\
>>   	 VM_ENTRY_LOAD_BNDCFGS |					\
>>   	 VM_ENTRY_PT_CONCEAL_PIP |					\
>> -	 VM_ENTRY_LOAD_IA32_RTIT_CTL)
>> +	 VM_ENTRY_LOAD_IA32_RTIT_CTL |					\
>> +	 VM_ENTRY_LOAD_CET_STATE)
>>   
>>   #define __KVM_REQUIRED_VMX_VM_EXIT_CONTROLS				\
>>   	(VM_EXIT_SAVE_DEBUG_CONTROLS |					\
>> @@ -502,7 +503,8 @@ static inline u8 vmx_get_rvi(void)
>>   	       VM_EXIT_LOAD_IA32_EFER |					\
>>   	       VM_EXIT_CLEAR_BNDCFGS |					\
>>   	       VM_EXIT_PT_CONCEAL_PIP |					\
>> -	       VM_EXIT_CLEAR_IA32_RTIT_CTL)
>> +	       VM_EXIT_CLEAR_IA32_RTIT_CTL |				\
>> +	       VM_EXIT_LOAD_CET_STATE)
>>   
>>   #define KVM_REQUIRED_VMX_PIN_BASED_VM_EXEC_CONTROL			\
>>   	(PIN_BASED_EXT_INTR_MASK |					\
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index c6b57ede0f57..2bcf3c7923bf 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -231,7 +231,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>>   				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>>   				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>>   
>> -#define KVM_SUPPORTED_XSS     0
>> +#define KVM_SUPPORTED_XSS	(XFEATURE_MASK_CET_USER | \
>> +				 XFEATURE_MASK_CET_KERNEL)
>>   
>>   u64 __read_mostly host_efer;
>>   EXPORT_SYMBOL_GPL(host_efer);
>> @@ -9854,6 +9855,15 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>>   	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
>>   		kvm_caps.supported_xss = 0;
>>   
>> +	if ((kvm_caps.supported_xss & (XFEATURE_MASK_CET_USER |
>> +	     XFEATURE_MASK_CET_KERNEL)) !=
>> +	    (XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)) {
>> +		kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
>> +		kvm_cpu_cap_clear(X86_FEATURE_IBT);
>> +		kvm_caps.supported_xss &= ~XFEATURE_CET_USER;
>> +		kvm_caps.supported_xss &= ~XFEATURE_CET_KERNEL;
>> +	}
>> +
>>   #define __kvm_cpu_cap_has(UNUSED_, f) kvm_cpu_cap_has(f)
>>   	cr4_reserved_bits = __cr4_reserved_bits(__kvm_cpu_cap_has, UNUSED_);
>>   #undef __kvm_cpu_cap_has
>> @@ -12319,7 +12329,9 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>>   
>>   static inline bool is_xstate_reset_needed(void)
>>   {
>> -	return kvm_cpu_cap_has(X86_FEATURE_MPX);
>> +	return kvm_cpu_cap_has(X86_FEATURE_MPX) ||
>> +	       kvm_cpu_cap_has(X86_FEATURE_SHSTK) ||
>> +	       kvm_cpu_cap_has(X86_FEATURE_IBT);
>>   }
>>   
>>   void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>> @@ -12396,6 +12408,16 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>   						       XFEATURE_BNDCSR);
>>   		}
>>   
>> +		if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
>> +			fpstate_clear_xstate_component(fpstate,
>> +						       XFEATURE_CET_USER);
>> +			fpstate_clear_xstate_component(fpstate,
>> +						       XFEATURE_CET_KERNEL);
>> +		} else if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
>> +			fpstate_clear_xstate_component(fpstate,
>> +						       XFEATURE_CET_USER);
>> +		}
>> +
>>   		if (init_event)
>>   			kvm_load_guest_fpu(vcpu);
>>   	}
>> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>> index d9cc352cf421..dc79dcd733ac 100644
>> --- a/arch/x86/kvm/x86.h
>> +++ b/arch/x86/kvm/x86.h
>> @@ -531,6 +531,9 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
>>   		__reserved_bits |= X86_CR4_VMXE;        \
>>   	if (!__cpu_has(__c, X86_FEATURE_PCID))          \
>>   		__reserved_bits |= X86_CR4_PCIDE;       \
>> +	if (!__cpu_has(__c, X86_FEATURE_SHSTK) &&       \
>> +	    !__cpu_has(__c, X86_FEATURE_IBT))           \
>> +		__reserved_bits |= X86_CR4_CET;         \
>>   	__reserved_bits;                                \
>>   })
>>   
>
> Best regards,
> 	Maxim Levitsky
>
>
>