Re: [PATCH v16 30/51] KVM: nVMX: Virtualize NO_HW_ERROR_CODE_CC for L1 event injection to L2

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

On 9/20/2025 6:32 AM, Sean Christopherson wrote:
> From: Yang Weijiang <weijiang.yang@intel.com>
>
> Per SDM description(Vol.3D, Appendix A.1):
> "If bit 56 is read as 1, software can use VM entry to deliver a hardware
> exception with or without an error code, regardless of vector"
>
> Modify has_error_code check before inject events to nested guest. Only
> enforce the check when guest is in real mode, the exception is not hard
> exception and the platform doesn't enumerate bit56 in VMX_BASIC, in all
> other case ignore the check to make the logic consistent with SDM.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Tested-by: Mathias Krause <minipli@grsecurity.net>
> Tested-by: John Allen <john.allen@amd.com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>

> ---
>   arch/x86/kvm/vmx/nested.c | 27 ++++++++++++++++++---------
>   arch/x86/kvm/vmx/nested.h |  5 +++++
>   2 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 846c07380eac..b644f4599f70 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -1272,9 +1272,10 @@ static int vmx_restore_vmx_basic(struct vcpu_vmx *vmx, u64 data)
>   {
>   	const u64 feature_bits = VMX_BASIC_DUAL_MONITOR_TREATMENT |
>   				 VMX_BASIC_INOUT |
> -				 VMX_BASIC_TRUE_CTLS;
> +				 VMX_BASIC_TRUE_CTLS |
> +				 VMX_BASIC_NO_HW_ERROR_CODE_CC;
>   
> -	const u64 reserved_bits = GENMASK_ULL(63, 56) |
> +	const u64 reserved_bits = GENMASK_ULL(63, 57) |
>   				  GENMASK_ULL(47, 45) |
>   				  BIT_ULL(31);
>   
> @@ -2949,7 +2950,6 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
>   		u8 vector = intr_info & INTR_INFO_VECTOR_MASK;
>   		u32 intr_type = intr_info & INTR_INFO_INTR_TYPE_MASK;
>   		bool has_error_code = intr_info & INTR_INFO_DELIVER_CODE_MASK;
> -		bool should_have_error_code;
>   		bool urg = nested_cpu_has2(vmcs12,
>   					   SECONDARY_EXEC_UNRESTRICTED_GUEST);
>   		bool prot_mode = !urg || vmcs12->guest_cr0 & X86_CR0_PE;
> @@ -2966,12 +2966,19 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
>   		    CC(intr_type == INTR_TYPE_OTHER_EVENT && vector != 0))
>   			return -EINVAL;
>   
> -		/* 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);
> -		if (CC(has_error_code != should_have_error_code))
> -			return -EINVAL;
> +		/*
> +		 * Cannot deliver error code in real mode or if the interrupt
> +		 * type is not hardware exception. For other cases, do the
> +		 * consistency check only if the vCPU doesn't enumerate
> +		 * VMX_BASIC_NO_HW_ERROR_CODE_CC.
> +		 */
> +		if (!prot_mode || intr_type != INTR_TYPE_HARD_EXCEPTION) {
> +			if (CC(has_error_code))
> +				return -EINVAL;
> +		} else if (!nested_cpu_has_no_hw_errcode_cc(vcpu)) {
> +			if (CC(has_error_code != x86_exception_has_error_code(vector)))
> +				return -EINVAL;
> +		}
>   
>   		/* VM-entry exception error code */
>   		if (CC(has_error_code &&
> @@ -7217,6 +7224,8 @@ static void nested_vmx_setup_basic(struct nested_vmx_msrs *msrs)
>   	msrs->basic |= VMX_BASIC_TRUE_CTLS;
>   	if (cpu_has_vmx_basic_inout())
>   		msrs->basic |= VMX_BASIC_INOUT;
> +	if (cpu_has_vmx_basic_no_hw_errcode_cc())
> +		msrs->basic |= VMX_BASIC_NO_HW_ERROR_CODE_CC;
>   }
>   
>   static void nested_vmx_setup_cr_fixed(struct nested_vmx_msrs *msrs)
> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
> index 6eedcfc91070..983484d42ebf 100644
> --- a/arch/x86/kvm/vmx/nested.h
> +++ b/arch/x86/kvm/vmx/nested.h
> @@ -309,6 +309,11 @@ static inline bool nested_cr4_valid(struct kvm_vcpu *vcpu, unsigned long val)
>   	       __kvm_is_valid_cr4(vcpu, val);
>   }
>   
> +static inline bool nested_cpu_has_no_hw_errcode_cc(struct kvm_vcpu *vcpu)
> +{
> +	return to_vmx(vcpu)->nested.msrs.basic & VMX_BASIC_NO_HW_ERROR_CODE_CC;
> +}
> +
>   /* No difference in the restrictions on guest and host CR4 in VMX operation. */
>   #define nested_guest_cr4_valid	nested_cr4_valid
>   #define nested_host_cr4_valid	nested_cr4_valid