x86/ioapic: Handle Extended Destination ID field in RTE

Bits 63-48 of the I/OAPIC Redirection Table Entry map directly to bits 19-4
of the address used in the resulting MSI cycle.

Historically, the x86 MSI format only used the top 8 of those 16 bits as
the destination APIC ID, and the "Extended Destination ID" in the lower 8
bits was unused.

With interrupt remapping, the lowest bit of the Extended Destination ID
(bit 48 of RTE, bit 4 of MSI address) is now used to indicate a remappable
format MSI.

A hypervisor can use the other 7 bits of the Extended Destination ID to
permit guests to address up to 15 bits of APIC IDs, thus allowing 32768
vCPUs before having to expose a vIOMMU and interrupt remapping to the
guest.

No behavioural change in this patch, since nothing yet permits APIC IDs
above 255 to be used with the non-IR I/OAPIC domain.

[ tglx: Converted it to the cleaned up entry/msi_msg format and added
commentry ]

Signed-off-by: David Woodhouse <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/include/asm/io_apic.h

···
 				is_level		:  1,
 				masked			:  1,
 				reserved_0		: 15,
-				reserved_1		: 24,
+				reserved_1		: 17,
+				virt_destid_8_14	:  7,
 				destid_0_7		:  8;
 		};
 		struct {

arch/x86/kernel/apic/io_apic.c

···
 			       (entry.ir_index_15 << 15) | entry.ir_index_0_14,
 				entry.ir_zero);
 		} else {
-			printk(KERN_DEBUG "%s, %s, D(%02X), M(%1d)\n", buf,
+			printk(KERN_DEBUG "%s, %s, D(%02X%02X), M(%1d)\n", buf,
 			       entry.dest_mode_logical ? "logical " : "physical",
-			       entry.destid_0_7, entry.delivery_mode);
+			       entry.virt_destid_8_14, entry.destid_0_7,
+			       entry.delivery_mode);
 		}
 	}
 }
···
 	 */
 	if (ioapic_i8259.pin != -1) {
 		struct IO_APIC_route_entry entry;
+		u32 apic_id = read_apic_id();
 
 		memset(&entry, 0, sizeof(entry));
 		entry.masked		= false;
···
 		entry.active_low	= false;
 		entry.dest_mode_logical	= false;
 		entry.delivery_mode	= APIC_DELIVERY_MODE_EXTINT;
-		entry.destid_0_7	= read_apic_id();
+		entry.destid_0_7	= apic_id & 0xFF;
+		entry.virt_destid_8_14	= apic_id >> 8;
 
 		/*
 		 * Add it to the IO-APIC irq-routing table:
···
 	/* DMAR/IR: 1, 0 for all other modes */
 	entry->ir_format		= msg.arch_addr_lo.dmar_format;
 	/*
-	 * DMAR/IR: index bit 0-14.
+	 * - DMAR/IR: index bit 0-14.
+	 *
+	 * - Virt: If the host supports x2apic without a virtualized IR
+	 *	   unit then bit 0-6 of dmar_index_0_14 are providing bit
+	 *	   8-14 of the destination id.
 	 *
 	 * All other modes have bit 0-6 of dmar_index_0_14 cleared and the
 	 * topmost 8 bits are destination id bit 0-7 (entry::destid_0_7).
···
 	int apic, pin, i;
 	struct IO_APIC_route_entry entry0, entry1;
 	unsigned char save_control, save_freq_select;
+	u32 apic_id;
 
 	pin  = find_isa_irq_pin(8, mp_INT);
 	if (pin == -1) {
···
 	entry0 = ioapic_read_entry(apic, pin);
 	clear_IO_APIC_pin(apic, pin);
 
+	apic_id = hard_smp_processor_id();
 	memset(&entry1, 0, sizeof(entry1));
 
 	entry1.dest_mode_logical	= true;
 	entry1.masked			= false;
-	entry1.destid_0_7		= hard_smp_processor_id();
+	entry1.destid_0_7		= apic_id & 0xFF;
+	entry1.virt_destid_8_14		= apic_id >> 8;
 	entry1.delivery_mode		= APIC_DELIVERY_MODE_EXTINT;
 	entry1.active_low		= entry0.active_low;
 	entry1.is_level			= false;