Re: [PATCH v2 10/21] KVM:x86: Add #CP support in guest exception classification

[Binbin Wu <binbin.wu@linux.intel.com>]

On 4/21/2023 9:46 PM, Yang Weijiang wrote:
> Add handling for Control Protection (#CP) exceptions(vector 21).
> The new vector is introduced for Intel's Control-Flow Enforcement
> Technology (CET) relevant violation cases.
> See Intel's SDM for details.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>   arch/x86/include/uapi/asm/kvm.h |  1 +
>   arch/x86/kvm/vmx/nested.c       |  2 +-
>   arch/x86/kvm/x86.c              | 10 +++++++---
>   arch/x86/kvm/x86.h              | 13 ++++++++++---
>   4 files changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index 7f467fe05d42..1c002abe2be8 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -33,6 +33,7 @@
>   #define MC_VECTOR 18
>   #define XM_VECTOR 19
>   #define VE_VECTOR 20
> +#define CP_VECTOR 21
>   
>   /* Select x86 specific features in <linux/kvm.h> */
>   #define __KVM_HAVE_PIT
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 96ede74a6067..7bc62cd72748 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2850,7 +2850,7 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
>   		/* VM-entry interruption-info field: deliver error code */
>   		should_have_error_code =
>   			intr_type == INTR_TYPE_HARD_EXCEPTION && prot_mode &&
> -			x86_exception_has_error_code(vector);
> +			x86_exception_has_error_code(vcpu, vector);
>   		if (CC(has_error_code != should_have_error_code))
>   			return -EINVAL;
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7788646bbf1f..a768cbf3fbb7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -520,11 +520,15 @@ EXPORT_SYMBOL_GPL(kvm_spurious_fault);
>   #define EXCPT_CONTRIBUTORY	1
>   #define EXCPT_PF		2
>   
> -static int exception_class(int vector)
> +static int exception_class(struct kvm_vcpu *vcpu, int vector)
>   {
>   	switch (vector) {
>   	case PF_VECTOR:
>   		return EXCPT_PF;
> +	case CP_VECTOR:
> +		if (vcpu->arch.cr4_guest_rsvd_bits & X86_CR4_CET)
> +			return EXCPT_BENIGN;
> +		return EXCPT_CONTRIBUTORY;
By definition, #CP is Contributory.
Can you explain more about this change here which treats #CP as 
EXCPT_BENIGN when CET is not enabled in guest?

In current KVM code, there is suppose no #CP triggered in guest if CET 
is not enalbed in guest, right?
>   	case DE_VECTOR:
>   	case TS_VECTOR:
>   	case NP_VECTOR:
> @@ -707,8 +711,8 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
>   		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
>   		return;
>   	}
> -	class1 = exception_class(prev_nr);
> -	class2 = exception_class(nr);
> +	class1 = exception_class(vcpu, prev_nr);
> +	class2 = exception_class(vcpu, nr);
>   	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY) ||
>   	    (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
>   		/*
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index c544602d07a3..2ba7c7fc4846 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -171,13 +171,20 @@ static inline bool is_64_bit_hypercall(struct kvm_vcpu *vcpu)
>   	return vcpu->arch.guest_state_protected || is_64_bit_mode(vcpu);
>   }
>   
> -static inline bool x86_exception_has_error_code(unsigned int vector)
> +static inline bool x86_exception_has_error_code(struct kvm_vcpu *vcpu,
> +						unsigned int vector)
>   {
>   	static u32 exception_has_error_code = BIT(DF_VECTOR) | BIT(TS_VECTOR) |
>   			BIT(NP_VECTOR) | BIT(SS_VECTOR) | BIT(GP_VECTOR) |
> -			BIT(PF_VECTOR) | BIT(AC_VECTOR);
> +			BIT(PF_VECTOR) | BIT(AC_VECTOR) | BIT(CP_VECTOR);
>   
> -	return (1U << vector) & exception_has_error_code;
> +	if (!((1U << vector) & exception_has_error_code))
> +		return false;
> +
> +	if (vector == CP_VECTOR)
> +		return !(vcpu->arch.cr4_guest_rsvd_bits & X86_CR4_CET);
> +
> +	return true;
>   }
>   
>   static inline bool mmu_is_nested(struct kvm_vcpu *vcpu)