[Xen-devel] [PATCH 6/9] arm: vgic: fix race in vgic_vcpu_inject_irq

[Ian Campbell <ijc@xxxxxxxxxxxxxx>]

From: Ian Campbell <ian.campbell@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 xen/arch/arm/vgic.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index dbfcd04..b30da78 100644
--- 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);
 
@@ -601,20 +606,18 @@ 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);
             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 */
-out:
     vcpu_unblock(v);
 }
 
-- 
1.7.10.4


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