xen: disable interrupts before saving in percpu
Impact: Fix race condition
xen_mc_batch has a small preempt race where it takes the address of a
percpu variable immediately before disabling interrupts, thereby
leaving a small window in which we may migrate to another cpu and save
the flags in the wrong percpu variable. Disable interrupts before
saving the old flags in a percpu.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/xen/multicalls.h b/arch/x86/xen/multicalls.h
index 8589382..fa3e107 100644
--- a/arch/x86/xen/multicalls.h
+++ b/arch/x86/xen/multicalls.h
@@ -19,8 +19,10 @@
paired with xen_mc_issue() */
static inline void xen_mc_batch(void)
{
+ unsigned long flags;
/* need to disable interrupts until this entry is complete */
- local_irq_save(__get_cpu_var(xen_mc_irq_flags));
+ local_irq_save(flags);
+ __get_cpu_var(xen_mc_irq_flags) = flags;
}
static inline struct multicall_space xen_mc_entry(size_t args)
