[PATCH v6 1/2] arm: remove irq from inflight, then change physical affinity

[Stefano Stabellini <sstabellini@kernel.org>]

This patch fixes a potential race that could happen when
gic_update_one_lr and vgic_vcpu_inject_irq run simultaneously.

When GIC_IRQ_GUEST_MIGRATING is set, we must make sure that the irq has
been removed from inflight before changing physical affinity, to avoid
concurrent accesses to p->inflight, as vgic_vcpu_inject_irq will take a
different vcpu lock.

Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>

---
 xen/arch/arm/gic.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index 9522c6c..de996d9 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -503,6 +503,11 @@ static void gic_update_one_lr(struct vcpu *v, int i)
             gic_raise_guest_irq(v, irq, p->priority);
         else {
             list_del_init(&p->inflight);
+            /* Remove from inflight, then change physical affinity. It
+             * makes sure that when a new interrupt is received on the
+             * next pcpu, inflight is already cleared. No concurrent
+             * accesses to inflight. */
+            smp_wmb();
             if ( test_and_clear_bit(GIC_IRQ_GUEST_MIGRATING, &p->status) )
             {
                 struct vcpu *v_target = vgic_get_target_vcpu(v, irq);
-- 
1.9.1


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