arm: vgic: fix race in vgic_vcpu_inject_irq

The initial check for a still pending interrupt (!list_empty(&n->inflight))
needs to be covered by the vgic lock to avoid trying to insert the IRQ into the
inflight list simultaneously on 2 pCPUS. Expand the area covered by the lock
appropriately.

Also consolidate the unlocks on the exit path into one location.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index d9ceaaaec0064791374bf8c7310e7992bc1e6e03..4d8da0242e307f1071c17a5452414be66bec9725 100644 (file)
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -584,9 +584,14 @@ void vgic_vcpu_inject_irq(struct vcpu *v, unsigned int irq, int virtual)
     struct pending_irq *iter, *n = irq_to_pending(v, irq);
     unsigned long flags;
 
-    /* irq still pending */
+    spin_lock_irqsave(&v->arch.vgic.lock, flags);
+
+    /* irq already pending */
     if (!list_empty(&n->inflight))
+    {
+        spin_unlock_irqrestore(&v->arch.vgic.lock, flags);
         return;
+    }
 
     priority = byte_read(rank->ipriority[REG_RANK_INDEX(8, idx)], 0, byte);
 
@@ -601,17 +606,16 @@ void vgic_vcpu_inject_irq(struct vcpu *v, unsigned int irq, int virtual)
     if ( rank->ienable & (1 << (irq % 32)) )
         gic_set_guest_irq(v, irq, GICH_LR_PENDING, priority);
 
-    spin_lock_irqsave(&v->arch.vgic.lock, flags);
     list_for_each_entry ( iter, &v->arch.vgic.inflight_irqs, inflight )
     {
         if ( iter->priority > priority )
         {
             list_add_tail(&n->inflight, &iter->inflight);
-            spin_unlock_irqrestore(&v->arch.vgic.lock, flags);
-            return;
+            goto out;
         }
     }
     list_add_tail(&n->inflight, &v->arch.vgic.inflight_irqs);
+out:
     spin_unlock_irqrestore(&v->arch.vgic.lock, flags);
     /* we have a new higher priority irq, inject it into the guest */
 }