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

Binbin Wu
2025-09-22T08:37:57Z

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