x86/tdx: Add SetupEventNotifyInterrupt TDX hypercall support

SetupEventNotifyInterrupt TDX hypercall is used by guest TD to specify
which interrupt vector to use as an event-notify vector to the VMM.
Such registered vector is also used by Host VMM to notify about
completion of GetQuote requests to the Guest TD.

Add tdx_hcall_set_notify_intr() helper function to implement the
SetupEventNotifyInterrupt hypercall.

This will be used by the TD quote driver.

Details about the SetupEventNotifyInterrupt TDVMCALL can be found in
TDX Guest-Host Communication Interface (GHCI) Specification, sec 3.5
"VP.VMCALL<SetupEventNotifyInterrupt>".

Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

arch/x86/kernel/tdx.c

@@ -24,6 +24,7 @@
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
 #define TDVMCALL_GET_QUOTE		0x10002
+#define TDVMCALL_SETUP_NOTIFY_INTR	0x10004
 
 /* See Exit Qualification for I/O Instructions in VMX documentation */
 #define VE_IS_IO_IN(exit_qual)		(((exit_qual) & 8) ? 1 : 0)
@@ -213,6 +214,37 @@ int tdx_hcall_get_quote(u64 data)
 }
 EXPORT_SYMBOL_GPL(tdx_hcall_get_quote);
 
+/*
+ * tdx_hcall_set_notify_intr() - Setup Event Notify Interrupt Vector.
+ *
+ * @vector        : Vector address to be used for notification.
+ *
+ * return 0 on success or failure error number.
+ */
+int tdx_hcall_set_notify_intr(u8 vector)
+{
+	u64 ret;
+
+	/* Minimum vector value allowed is 32 */
+	if (vector < 32)
+		return -EINVAL;
+
+	/*
+	 * Register callback vector address with VMM. More details
+	 * about the ABI can be found in TDX Guest-Host-Communication
+	 * Interface (GHCI), sec 3.5.
+	 */
+	ret = _trace_tdx_hypercall(TDVMCALL_SETUP_NOTIFY_INTR, vector, 0, 0, 0,
+				   NULL);
+
+	if (ret == TDVMCALL_SUCCESS)
+		return 0;
+	else if (ret == TDCALL_INVALID_OPERAND)
+		return -EINVAL;
+
+	return -EIO;
+}
+
 static void tdx_get_info(void)
 {
 	struct tdx_module_output out;