queue-2.6.33/xen-smp-warn-user-why-they-keel-over-nosmp-or-noapic-and-what-to-use-instead.patch

From ed467e69f16e6b480e2face7bc5963834d025f91 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Thu, 1 Sep 2011 09:48:27 -0400
Subject: xen/smp: Warn user why they keel over - nosmp or noapic and what to use instead.

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

commit ed467e69f16e6b480e2face7bc5963834d025f91 upstream.

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

Acked-by: Ian Campbell <Ian.Campbell@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 arch/x86/xen/smp.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -30,6 +30,7 @@
 #include <xen/page.h>
 #include <xen/events.h>
 
+#include <xen/hvc-console.h>
 #include "xen-ops.h"
 #include "mmu.h"
 
@@ -180,6 +181,15 @@ static void __init xen_smp_prepare_cpus(
 {
 	unsigned cpu;
 
+	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);