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

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@gmail.com>
Link: https://patch.msgid.link/aiHnI1mu6SGQrgnz@v4bel
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org

diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 70a161383e5a6078ea1012a84e1e081e3cec088d..ccb7e3a90cd07a9f84202ce65600ea6ceef27524 100644 (file)
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -820,15 +820,16 @@ retry:
                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);