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

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Message-ID: <Z6sNVHulm4Lovz2T@intel.com>
Date: Tue, 11 Feb 2025 16:41:56 +0800
From: Chao Gao <chao.gao@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>, <kvm@...r.kernel.org>,
	<rick.p.edgecombe@...el.com>, <kai.huang@...el.com>,
	<adrian.hunter@...el.com>, <reinette.chatre@...el.com>,
	<xiaoyao.li@...el.com>, <tony.lindgren@...el.com>,
	<isaku.yamahata@...el.com>, <yan.y.zhao@...el.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/8] KVM: TDX: Add a place holder for handler of TDX
 hypercalls (TDG.VP.VMCALL)

>+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?

I think we should do the conversion for leafs that are defined in the current
GHCI spec.

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