io_apic: Support APIC Extended Destination IDs

If APIC Extended Destination ID support is enabled, use it in APIC RTEs
by allowing APIC IDs up to 2^15 - 1 and encoding the high bits into
Intel "reserved" bits per the standard.

Reviewed by:	kib
MFC after:	3 weeks
Sponsored by:	Amazon
Differential Revision:	https://reviews.freebsd.org/D55889

sys/x86/include/apicvar.h

@@ -84,6 +84,7 @@
  * to use that ID.
  */
 #define	IOAPIC_MAX_ID		0xff
+#define	IOAPIC_MAX_EXT_ID	0x7fff
 
 /* I/O Interrupts are used for external devices such as ISA, PCI, etc. */
 #define	APIC_IO_INTS	(IDT_IO_INTS + 16)

sys/x86/x86/io_apic.c

@@ -371,6 +371,13 @@ ioapic_program_intpin(struct ioapic_intsrc *intpin)
 		low = IOART_DESTPHY;
 		high = intpin->io_cpu << APIC_ID_SHIFT;
 		intpin->io_valid = 1;
+	} else if (intpin->io_cpu <= IOAPIC_MAX_EXT_ID &&
+	    apic_ext_dest_id == 1) {
+		low = IOART_DESTPHY;
+		high = intpin->io_cpu << APIC_ID_SHIFT & APIC_ID_MASK;
+		high |= (intpin->io_cpu >> 8) << APIC_EXT_ID_SHIFT
+		    & APIC_EXT_ID_MASK;
+		intpin->io_valid = 1;
 	} else {
 		printf("%s: unsupported destination APIC ID %u for pin %u\n",
 		    __func__, intpin->io_cpu, intpin->io_intpin);