KVM: TDX: Handle TDG.VP.VMCALL<GetTdVmCallInfo> hypercall

Implement TDG.VP.VMCALL<GetTdVmCallInfo> hypercall.  If the input value is
zero, return success code and zero in output registers.

TDG.VP.VMCALL<GetTdVmCallInfo> hypercall is a subleaf of TDG.VP.VMCALL to
enumerate which TDG.VP.VMCALL sub leaves are supported.  This hypercall is
for future enhancement of the Guest-Host-Communication Interface (GHCI)
specification.  The GHCI version of 344426-001US defines it to require
input R12 to be zero and to return zero in output registers, R11, R12, R13,
and R14 so that guest TD enumerates no enhancement.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Message-ID: <20250227012021.1778144-12-binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: yamahata

arch/x86/include/asm/shared/tdx.h

@@ -67,6 +67,7 @@
 #define TD_CTLS_LOCK			BIT_ULL(TD_CTLS_LOCK_BIT)
 
 /* TDX hypercall Leaf IDs */
+#define TDVMCALL_GET_TD_VM_CALL_INFO	0x10000
 #define TDVMCALL_MAP_GPA		0x10001
 #define TDVMCALL_GET_QUOTE		0x10002
 #define TDVMCALL_REPORT_FATAL_ERROR	0x10003

arch/x86/kvm/vmx/tdx.c

@@ -1448,13 +1448,29 @@ static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static int tdx_get_td_vm_call_info(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+
+	if (tdx->vp_enter_args.r12)
+		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
+	else {
+		tdx->vp_enter_args.r11 = 0;
+		tdx->vp_enter_args.r13 = 0;
+		tdx->vp_enter_args.r14 = 0;
+	}
+	return 1;
+}
+
 static int handle_tdvmcall(struct kvm_vcpu *vcpu)
 {
 	switch (tdvmcall_leaf(vcpu)) {
 	case TDVMCALL_MAP_GPA:
 		return tdx_map_gpa(vcpu);
 	case TDVMCALL_REPORT_FATAL_ERROR:
 		return tdx_report_fatal_error(vcpu);
+	case TDVMCALL_GET_TD_VM_CALL_INFO:
+		return tdx_get_td_vm_call_info(vcpu);
 	default:
 		break;
 	}