x86, irq: get nr_irqs from madt

Until now, NR_IRQS was derived from black magic defines that had to
be "large enough" to both accomodate NR_CPUS and MAX_NR_IO_APICs.

This resulted in a way too large irq_desc[] array on most x86 systems.
Especially with larger CPU masks, the size of irq_desc can spiral out
of control quickly.

So be smarter about it and use precise allocation instead: determine the
default maximum possible IRQ number from the ACPI MADT. Use a minimum limit
of at least 32 IRQs for broken BIOSes.
Signed-off-by: NYinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/acpi/boot.c

@@ -957,6 +957,29 @@ void __init mp_register_ioapic(int id, u32 address, u32 gsi_base)
 	nr_ioapics++;
 }
 
+int get_nr_irqs_via_madt(void)
+{
+	int idx;
+	int nr = 0;
+
+	for (idx = 0; idx < nr_ioapics; idx++) {
+		if (mp_ioapic_routing[idx].gsi_end > nr)
+			nr = mp_ioapic_routing[idx].gsi_end;
+	}
+
+	nr++;
+
+	/* double it for hotplug and msi and nmi */
+	nr <<= 1;
+
+	/* something wrong ? */
+	if (nr < 32)
+		nr = 32;
+
+	return nr;
+
+}
+
 static void assign_to_mp_irq(struct mp_config_intsrc *m,
 				    struct mp_config_intsrc *mp_irq)
 {
@@ -1254,9 +1277,12 @@ static int __init acpi_parse_madt_ioapic_entries(void)
 		return count;
 	}
 
+
+	nr_irqs = get_nr_irqs_via_madt();
+
 	count =
 	    acpi_table_parse_madt(ACPI_MADT_TYPE_INTERRUPT_OVERRIDE, acpi_parse_int_src_ovr,
-				  NR_IRQ_VECTORS);
+				  nr_irqs);
 	if (count < 0) {
 		printk(KERN_ERR PREFIX
 		       "Error parsing interrupt source overrides entry\n");
@@ -1276,7 +1302,7 @@ static int __init acpi_parse_madt_ioapic_entries(void)
 
 	count =
 	    acpi_table_parse_madt(ACPI_MADT_TYPE_NMI_SOURCE, acpi_parse_nmi_src,
-				  NR_IRQ_VECTORS);
+				  nr_irqs);
 	if (count < 0) {
 		printk(KERN_ERR PREFIX "Error parsing NMI SRC entry\n");
 		/* TBD: Cleanup to allow fallback to MPS */

include/asm-x86/mpspec.h

@@ -60,6 +60,7 @@ extern void mp_override_legacy_irq(u8 bus_irq, u8 polarity, u8 trigger,
 				   u32 gsi);
 extern void mp_config_acpi_legacy_irqs(void);
 extern int mp_register_gsi(u32 gsi, int edge_level, int active_high_low);
+extern int get_nr_irqs_via_madt(void);
 #ifdef CONFIG_X86_IO_APIC
 extern int mp_config_acpi_gsi(unsigned char number, unsigned int devfn, u8 pin,
 				u32 gsi, int triggering, int polarity);