[PATCH 1/2] kvm: leverage change to adjust slots->used_slots in update_memslots()

[Wei Yang <richard.weiyang@xxxxxxxxx>]

update_memslots() is only called by __kvm_set_memory_region(), in which
change is calculated to indicate the following behavior. With this
information, it is not necessary to do the calculation again in
update_memslots().

By encoding the number of slot adjustment in the lowest byte of change,
the slots->used_slots adjustment is accomplished by one addition.

Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
---
 include/linux/kvm_host.h | 11 +++++++----
 virt/kvm/kvm_main.c      | 14 ++++----------
 2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4ee7bc548a83..e0ae6cf82c0d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -610,12 +610,15 @@ id_to_memslot(struct kvm_memslots *slots, int id)
  *
  * Since flags can be changed by some of these operations, the following
  * differentiation is the best we can do for __kvm_set_memory_region():
+ *
+ * Encode the number of slot adjustment in the lowest byte, which will
+ * be used in update_memslots().
  */
 enum kvm_mr_change {
-	KVM_MR_CREATE,
-	KVM_MR_DELETE,
-	KVM_MR_MOVE,
-	KVM_MR_FLAGS_ONLY,
+	KVM_MR_CREATE     = 0x0001,
+	KVM_MR_DELETE     = 0x00ff,
+	KVM_MR_MOVE       = 0x0000,
+	KVM_MR_FLAGS_ONLY = 0x0100,
 };
 
 int kvm_set_memory_region(struct kvm *kvm,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3d233ebfbee9..5c1911790f25 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -801,21 +801,15 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
  * sorted array and known changed memslot position.
  */
 static void update_memslots(struct kvm_memslots *slots,
-			    struct kvm_memory_slot *new)
+			    struct kvm_memory_slot *new,
+			    enum kvm_mr_change change)
 {
 	int id = new->id;
 	int i = slots->id_to_index[id];
 	struct kvm_memory_slot *mslots = slots->memslots;
 
 	WARN_ON(mslots[i].id != id);
-	if (!new->npages) {
-		WARN_ON(!mslots[i].npages);
-		if (mslots[i].npages)
-			slots->used_slots--;
-	} else {
-		if (!mslots[i].npages)
-			slots->used_slots++;
-	}
+	slots->used_slots += (char)change;
 
 	while (i < KVM_MEM_SLOTS_NUM - 1 &&
 	       new->base_gfn <= mslots[i + 1].base_gfn) {
@@ -1050,7 +1044,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		memset(&new.arch, 0, sizeof(new.arch));
 	}
 
-	update_memslots(slots, &new);
+	update_memslots(slots, &new, change);
 	old_memslots = install_new_memslots(kvm, as_id, slots);
 
 	kvm_arch_commit_memory_region(kvm, mem, &old, &new, change);
-- 
2.15.1