[PATCH v3 6/6] KVM: Assert that slots_lock is held when resetting per-vCPU dirty rings

[Sean Christopherson]

Assert that slots_lock is held in kvm_dirty_ring_reset() and add a comment
to explain _why_ slots needs to be held for the duration of the reset.

Link: https://lore.kernel.org/all/aCSns6Q5oTkdXUEe@xxxxxxxxxx
Suggested-by: James Houghton <jthoughton@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 virt/kvm/dirty_ring.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index 54734025658a..1ba02a06378c 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -122,6 +122,14 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
 	unsigned long mask = 0;
 	struct kvm_dirty_gfn *entry;
 
+	/*
+	 * Ensure concurrent calls to KVM_RESET_DIRTY_RINGS are serialized,
+	 * e.g. so that KVM fully resets all entries processed by a given call
+	 * before returning to userspace.  Holding slots_lock also protects
+	 * the various memslot accesses.
+	 */
+	lockdep_assert_held(&kvm->slots_lock);
+
 	while (likely((*nr_entries_reset) < INT_MAX)) {
 		if (signal_pending(current))
 			return -EINTR;
-- 
2.49.0.1112.g889b7c5bd8-goog