xen/mmu: weaken flush_tlb_other test

Impact: fixes crashing bug

There's no particular problem with getting an empty cpu mask,
so just shortcut-return if we get one.

Avoids crash reported by Christophe Saout <christophe@saout.de>

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index df87c803cec..e425a32e0a9 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1293,8 +1293,8 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
         } *args;
         struct multicall_space mcs;
 
-        BUG_ON(cpumask_empty(cpus));
-        BUG_ON(!mm);
+        if (cpumask_empty(cpus))
+                return;         /* nothing to do */
 
         mcs = xen_mc_entry(sizeof(*args));
         args = mcs.args;