KVM: MMU: clear unsync_child_bitmap completely

In current code, some page's unsync_child_bitmap is not cleared completely
in mmu_sync_children(), for example, if two PDPEs shard one PDT, one of
PDPE's unsync_child_bitmap is not cleared.

Currently, it not harm anything just little overload, but it's the prepare
work for the later patch
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/mmu.c

@@ -1149,10 +1149,12 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
 	int i, ret, nr_unsync_leaf = 0;
 
 	for_each_unsync_children(sp->unsync_child_bitmap, i) {
+		struct kvm_mmu_page *child;
 		u64 ent = sp->spt[i];
 
-		if (is_shadow_present_pte(ent) && !is_large_pte(ent)) {
-			struct kvm_mmu_page *child;
+		if (!is_shadow_present_pte(ent) || is_large_pte(ent))
+			goto clear_child_bitmap;
+
 		child = page_header(ent & PT64_BASE_ADDR_MASK);
 
 		if (child->unsync_children) {
@@ -1160,22 +1162,25 @@ static int __mmu_unsync_walk(struct kvm_mmu_page *sp,
 				return -ENOSPC;
 
 			ret = __mmu_unsync_walk(child, pvec);
-				if (!ret) {
-					__clear_bit(i, sp->unsync_child_bitmap);
-					sp->unsync_children--;
-					WARN_ON((int)sp->unsync_children < 0);
-				} else if (ret > 0)
+			if (!ret)
+				goto clear_child_bitmap;
+			else if (ret > 0)
 				nr_unsync_leaf += ret;
 			else
 				return ret;
-			}
-
-			if (child->unsync) {
+		} else if (child->unsync) {
 			nr_unsync_leaf++;
 			if (mmu_pages_add(pvec, child, i))
 				return -ENOSPC;
-			}
-		}
+		} else
+			 goto clear_child_bitmap;
+
+		continue;
+
+clear_child_bitmap:
+		__clear_bit(i, sp->unsync_child_bitmap);
+		sp->unsync_children--;
+		WARN_ON((int)sp->unsync_children < 0);
 	}