KVM: arm/arm64: Properly protect VGIC locks from IRQs

As Jan reported [1], lockdep complains about the VGIC not being bullet
proof. This seems to be due to two issues:
- When commit 006df0f34930 ("KVM: arm/arm64: Support calling
  vgic_update_irq_pending from irq context") promoted irq_lock and
  ap_list_lock to _irqsave, we forgot two instances of irq_lock.
  lockdeps seems to pick those up.
- If a lock is _irqsave, any other locks we take inside them should be
  _irqsafe as well. So the lpi_list_lock needs to be promoted also.

This fixes both issues by simply making the remaining instances of those
locks _irqsave.
One irq_lock is addressed in a separate patch, to simplify backporting.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/575718.html

Cc: stable@vger.kernel.org
Fixes: 006df0f34930 ("KVM: arm/arm64: Support calling vgic_update_irq_pending from irq context")
Reported-by: Jan Glauber <jan.glauber@caviumnetworks.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
index 97bfba8d9a59..33c8325c8f35 100644
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -43,9 +43,13 @@ struct vgic_global kvm_vgic_global_state __ro_after_init = {
  * kvm->lock (mutex)
  *   its->cmd_lock (mutex)
  *     its->its_lock (mutex)
- *       vgic_cpu->ap_list_lock
- *         kvm->lpi_list_lock
- *           vgic_irq->irq_lock
+ *       vgic_cpu->ap_list_lock		must be taken with IRQs disabled
+ *         kvm->lpi_list_lock		must be taken with IRQs disabled
+ *           vgic_irq->irq_lock		must be taken with IRQs disabled
+ *
+ * As the ap_list_lock might be taken from the timer interrupt handler,
+ * we have to disable IRQs before taking this lock and everything lower
+ * than it.
  *
  * If you need to take multiple locks, always take the upper lock first,
  * then the lower ones, e.g. first take the its_lock, then the irq_lock.
@@ -72,8 +76,9 @@ static struct vgic_irq *vgic_get_lpi(struct kvm *kvm, u32 intid)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
 	struct vgic_irq *irq = NULL;
+	unsigned long flags;
 
-	spin_lock(&dist->lpi_list_lock);
+	spin_lock_irqsave(&dist->lpi_list_lock, flags);
 
 	list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
 		if (irq->intid != intid)
@@ -89,7 +94,7 @@ static struct vgic_irq *vgic_get_lpi(struct kvm *kvm, u32 intid)
 	irq = NULL;
 
 out_unlock:
-	spin_unlock(&dist->lpi_list_lock);
+	spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
 
 	return irq;
 }
@@ -134,19 +139,20 @@ static void vgic_irq_release(struct kref *ref)
 void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
 {
 	struct vgic_dist *dist = &kvm->arch.vgic;
+	unsigned long flags;
 
 	if (irq->intid < VGIC_MIN_LPI)
 		return;
 
-	spin_lock(&dist->lpi_list_lock);
+	spin_lock_irqsave(&dist->lpi_list_lock, flags);
 	if (!kref_put(&irq->refcount, vgic_irq_release)) {
-		spin_unlock(&dist->lpi_list_lock);
+		spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
 		return;
 	};
 
 	list_del(&irq->lpi_list);
 	dist->lpi_list_count--;
-	spin_unlock(&dist->lpi_list_lock);
+	spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
 
 	kfree(irq);
 }