x86: fix probe_nr_irqs for xen

otherwise Xen is _completely_ unusable with 5 or more VCPUs.
(when !CONFIG_HAVE_SPARSE_IRQ).

based on Alex Nixon's patch.

also add +1 offset after redir_entries

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Alex Nixon <alex.nixon@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 3 deletions

diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
index 4e44fd1f466e..d28128e0392c 100644
--- a/arch/x86/kernel/io_apic.c
+++ b/arch/x86/kernel/io_apic.c
@@ -3625,16 +3625,21 @@ int __init probe_nr_irqs(void)
 {
         int idx;
         int nr = 0;
+#ifndef CONFIG_XEN
+        int nr_min = 32;
+#else
+        int nr_min = NR_IRQS;
+#endif
 
         for (idx = 0; idx < nr_ioapics; idx++)
-                nr += io_apic_get_redir_entries(idx);
+                nr += io_apic_get_redir_entries(idx) + 1;
 
         /* double it for hotplug and msi and nmi */
         nr <<= 1;
 
         /* something wrong ? */
-        if (nr < 32)
-                nr = 32;
+        if (nr < nr_min)
+                nr = nr_min;
 
         return nr;
 }