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: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 28 insertions, 2 deletions

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index eb875cdc736..3e9d163fd92 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/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 */