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Diffstat (limited to 'arch/x86/xen/irq.c')
-rw-r--r--arch/x86/xen/irq.c25
1 files changed, 12 insertions, 13 deletions
diff --git a/arch/x86/xen/irq.c b/arch/x86/xen/irq.c
index 01a4dc015ae..0da7f863056 100644
--- a/arch/x86/xen/irq.c
+++ b/arch/x86/xen/irq.c
@@ -47,23 +47,18 @@ static void xen_restore_fl(unsigned long flags)
/* convert from IF type flag */
flags = !(flags & X86_EFLAGS_IF);
- /* There's a one instruction preempt window here. We need to
- make sure we're don't switch CPUs between getting the vcpu
- pointer and updating the mask. */
+ /* See xen_irq_enable() for why preemption must be disabled. */
preempt_disable();
vcpu = this_cpu_read(xen_vcpu);
vcpu->evtchn_upcall_mask = flags;
- preempt_enable_no_resched();
-
- /* Doesn't matter if we get preempted here, because any
- pending event will get dealt with anyway. */
if (flags == 0) {
- preempt_check_resched();
barrier(); /* unmask then check (avoid races) */
if (unlikely(vcpu->evtchn_upcall_pending))
xen_force_evtchn_callback();
- }
+ preempt_enable();
+ } else
+ preempt_enable_no_resched();
}
PV_CALLEE_SAVE_REGS_THUNK(xen_restore_fl);
@@ -82,10 +77,12 @@ static void xen_irq_enable(void)
{
struct vcpu_info *vcpu;
- /* We don't need to worry about being preempted here, since
- either a) interrupts are disabled, so no preemption, or b)
- the caller is confused and is trying to re-enable interrupts
- on an indeterminate processor. */
+ /*
+ * We may be preempted as soon as vcpu->evtchn_upcall_mask is
+ * cleared, so disable preemption to ensure we check for
+ * events on the VCPU we are still running on.
+ */
+ preempt_disable();
vcpu = this_cpu_read(xen_vcpu);
vcpu->evtchn_upcall_mask = 0;
@@ -96,6 +93,8 @@ static void xen_irq_enable(void)
barrier(); /* unmask then check (avoid races) */
if (unlikely(vcpu->evtchn_upcall_pending))
xen_force_evtchn_callback();
+
+ preempt_enable();
}
PV_CALLEE_SAVE_REGS_THUNK(xen_irq_enable);