[Xen-devel] [PATCH 1/3] x86/xen: use memory barriers when enabling local irqs

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>

Because vcpu->evtchn_upcall_mask and vcpu->evtchn_upcall_pending are
be written by Xen as well as the guest, using barrier() (a
compiler-only barrier) in xen_enable_irq() and xen_restore_fl() is not
sufficient.

Use mb() (a full memory barrier) instead.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 arch/x86/xen/irq.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/irq.c b/arch/x86/xen/irq.c
index 01a4dc0..1a8d0d4 100644
--- a/arch/x86/xen/irq.c
+++ b/arch/x86/xen/irq.c
@@ -60,7 +60,7 @@ static void xen_restore_fl(unsigned long flags)
 
        if (flags == 0) {
                preempt_check_resched();
-               barrier(); /* unmask then check (avoid races) */
+               mb(); /* unmask then check (avoid races) */
                if (unlikely(vcpu->evtchn_upcall_pending))
                        xen_force_evtchn_callback();
        }
@@ -93,7 +93,7 @@ static void xen_irq_enable(void)
        /* Doesn't matter if we get preempted here, because any
           pending event will get dealt with anyway. */
 
-       barrier(); /* unmask then check (avoid races) */
+       mb(); /* unmask then check (avoid races) */
        if (unlikely(vcpu->evtchn_upcall_pending))
                xen_force_evtchn_callback();
 }
-- 
1.7.2.5


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