xen/smp: Warn user why they keel over - nosmp or noapic and what to use instead.

We have hit a couple of customer bugs where they would like to
use those parameters to run an UP kernel - but both of those
options turn of important sources of interrupt information so
we end up not being able to boot. The correct way is to
pass in 'dom0_max_vcpus=1' on the Xen hypervisor line and
the kernel will patch itself to be a UP kernel.

Fixes bug: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=637308

CC: stable@kernel.org
Acked-by: Ian Campbell <Ian.Campbell@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index e79dbb9..d4fc6d4 100644 (file)
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -32,6 +32,7 @@
 #include <xen/page.h>
 #include <xen/events.h>
 
+#include <xen/hvc-console.h>
 #include "xen-ops.h"
 #include "mmu.h"
 
@@ -207,6 +208,15 @@ static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
        unsigned cpu;
        unsigned int i;
 
+       if (skip_ioapic_setup) {
+               char *m = (max_cpus == 0) ?
+                       "The nosmp parameter is incompatible with Xen; " \
+                       "use Xen dom0_max_vcpus=1 parameter" :
+                       "The noapic parameter is incompatible with Xen";
+
+               xen_raw_printk(m);
+               panic(m);
+       }
        xen_init_lock_cpu(0);
 
        smp_store_cpu_info(0);