Re: [PATCH v6 24/25] KVM: nVMX: Introduce new VMX_BASIC bit for event error_code delivery to L1

[Yang, Weijiang]

On 11/1/2023 12:21 PM, Chao Gao wrote:
> On Thu, Sep 14, 2023 at 02:33:24AM -0400, Yang Weijiang wrote:
> > 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@xxxxxxxxx>
> > ---
> > arch/x86/kvm/vmx/nested.c | 22 ++++++++++++++--------
> > arch/x86/kvm/vmx/nested.h |  5 +++++
> > 2 files changed, 19 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index c5ec0ef51ff7..78a3be394d00 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -1205,9 +1205,9 @@ static int vmx_restore_vmx_basic(struct vcpu_vmx *vmx, u64 data)
> > {
> > 	const u64 feature_and_reserved =
> > 		/* feature (except bit 48; see below) */
> > -		BIT_ULL(49) | BIT_ULL(54) | BIT_ULL(55) |
> > +		BIT_ULL(49) | BIT_ULL(54) | BIT_ULL(55) | BIT_ULL(56) |
> > 		/* reserved */
> > -		BIT_ULL(31) | GENMASK_ULL(47, 45) | GENMASK_ULL(63, 56);
> > +		BIT_ULL(31) | GENMASK_ULL(47, 45) | GENMASK_ULL(63, 57);
> > 	u64 vmx_basic = vmcs_config.nested.basic;
> >
> > 	if (!is_bitwise_subset(vmx_basic, data, feature_and_reserved))
> > @@ -2846,12 +2846,16 @@ 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;
> > +		if (!prot_mode || intr_type != INTR_TYPE_HARD_EXCEPTION ||
> > +		    !nested_cpu_has_no_hw_errcode_cc(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);
> > +			if (CC(has_error_code != should_have_error_code))
> > +				return -EINVAL;
> > +		}
> prot_mode and intr_type are used twice, making the code a little hard to read.
>
> how about:
> 		/*
> 		 * Cannot deliver error code in real mode or if the
> 		 * interruption 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;
> 		}
>
> and drop should_have_error_code.

The change looks clearer, I'll take it, thanks!