[PATCH] KVM: Discard zero mask with function kvm_dirty_ring_reset

[Bibo Mao]

Function kvm_reset_dirty_gfn may be called with parameters cur_slot /
cur_offset / mask are all zero, it does not represent real dirty page.
It is not necessary to clear dirty page in this condition. Also return
value of macro __fls() is undefined if mask is zero which is called in
funciton kvm_reset_dirty_gfn(). Here just discard it.

Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
---
 virt/kvm/dirty_ring.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index 86d267db87bb..05f4c1c40cc7 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -147,14 +147,16 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring)
 				continue;
 			}
 		}
-		kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);
+		if (mask)
+			kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);
 		cur_slot = next_slot;
 		cur_offset = next_offset;
 		mask = 1;
 		first_round = false;
 	}
 
-	kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);
+	if (mask)
+		kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);
 
 	/*
 	 * The request KVM_REQ_DIRTY_RING_SOFT_FULL will be cleared

base-commit: 83a7eefedc9b56fe7bfeff13b6c7356688ffa670
-- 
2.39.3