Re: [PATCH v2 3/8] KVM: TDX: Add a place holder for handler of TDX hypercalls (TDG.VP.VMCALL)

[Binbin Wu]

On 2/11/2025 4:41 PM, Chao Gao wrote:
> > +static __always_inline unsigned long tdvmcall_exit_type(struct kvm_vcpu *vcpu)
> > +{
> > +	return to_tdx(vcpu)->vp_enter_args.r10;
> > +}
> please add a newline here.
>
> > +static __always_inline unsigned long tdvmcall_leaf(struct kvm_vcpu *vcpu)
> > +{
> > +	return to_tdx(vcpu)->vp_enter_args.r11;
> > +}
> ..
>
> > +static __always_inline void tdvmcall_set_return_code(struct kvm_vcpu *vcpu,
> > +						     long val)
> > +{
> > +	to_tdx(vcpu)->vp_enter_args.r10 = val;
> > +}
> ditto.
>
> > +static __always_inline void tdvmcall_set_return_val(struct kvm_vcpu *vcpu,
> > +						    unsigned long val)
> > +{
> > +	to_tdx(vcpu)->vp_enter_args.r11 = val;
> > +}
> > +
> > static inline void tdx_hkid_free(struct kvm_tdx *kvm_tdx)
> > {
> > 	tdx_guest_keyid_free(kvm_tdx->hkid);
> > @@ -810,6 +829,7 @@ static bool tdx_guest_state_is_invalid(struct kvm_vcpu *vcpu)
> > static __always_inline u32 tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
> > {
> > 	struct vcpu_tdx *tdx = to_tdx(vcpu);
> > +	u32 exit_reason;
> >
> > 	switch (tdx->vp_enter_ret & TDX_SEAMCALL_STATUS_MASK) {
> > 	case TDX_SUCCESS:
> > @@ -822,7 +842,21 @@ static __always_inline u32 tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
> > 		return -1u;
> > 	}
> >
> > -	return tdx->vp_enter_ret;
> > +	exit_reason = tdx->vp_enter_ret;
> > +
> > +	switch (exit_reason) {
> > +	case EXIT_REASON_TDCALL:
> > +		if (tdvmcall_exit_type(vcpu))
> > +			return EXIT_REASON_VMCALL;
> > +
> > +		if (tdvmcall_leaf(vcpu) < 0x10000)
> Can you add a comment for the hard-coded 0x10000?
>
> I am wondering what would happen if the guest tries to make a tdvmcall with
> leaf=0 or leaf=1 to mislead KVM into calling the NMI/interrupt handling
> routine. Would it trigger the unknown NMI warning or effectively inject an
> interrupt into the host?
Oh, yes, it's possible.

> I think we should do the conversion for leafs that are defined in the current
> GHCI spec.
Yes, it should be limited to the supported leaves defined in the GHCI.
Thanks for pointing it out!

> > +			return tdvmcall_leaf(vcpu);
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +
> > +	return exit_reason;
> > }