[PATCH] KVM: arm64: vgic: Check the interrupt is still ours before migrating it

[Hyunwoo Kim]

vgic_prune_ap_list() drops both ap_list_lock and irq_lock while migrating
an interrupt to another vCPU. After reacquiring the locks it only checks
that the affinity is unchanged (target_vcpu == vgic_target_oracle(irq))
before moving the interrupt, which assumes that an interrupt whose affinity
is preserved is still queued on this vCPU's ap_list.

That assumption no longer holds if the interrupt is taken off the ap_list
while the locks are dropped. vgic_flush_pending_lpis() removes the
interrupt from the list and sets irq->vcpu to NULL, but leaves
enabled/pending/target_vcpu untouched. As the interrupt is still enabled
and pending, vgic_target_oracle() returns the same target_vcpu, so the
affinity check passes and list_del() is run a second time on an entry that
has already been removed.

Also check that the interrupt is still assigned to this vCPU
(irq->vcpu == vcpu) before moving it.

Fixes: 0919e84c0fc1 ("KVM: arm/arm64: vgic-new: Add IRQ sync/flush framework")
Signed-off-by: Hyunwoo Kim <imv4bel at gmail.com>
---
 arch/arm64/kvm/vgic/vgic.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 1e9fe8764584..18b280de9a29 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -818,15 +818,16 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
 		raw_spin_lock(&irq->irq_lock);
 
 		/*
-		 * If the affinity has been preserved, move the
-		 * interrupt around. Otherwise, it means things have
-		 * changed while the interrupt was unlocked, and we
-		 * need to replay this.
+		 * If the interrupt is still ours and its affinity has
+		 * been preserved, move it around. Otherwise, it means
+		 * things have changed while the interrupt was unlocked
+		 * (it may even have been taken off the list with its
+		 * affinity left untouched), and we need to replay this.
 		 *
 		 * In all cases, we cannot trust the list not to have
 		 * changed, so we restart from the beginning.
 		 */
-		if (target_vcpu == vgic_target_oracle(irq)) {
+		if (irq->vcpu == vcpu && target_vcpu == vgic_target_oracle(irq)) {
 			struct vgic_cpu *new_cpu = &target_vcpu->arch.vgic_cpu;
 
 			list_del(&irq->ap_list);
-- 
2.43.0