KVM: Write protect the updated slot only when dirty logging is enabled

Calling kvm_mmu_slot_remove_write_access() for a deleted slot does
nothing but search for non-existent mmu pages which have mappings to
that deleted memory; this is safe but a waste of time.

Since we want to make the function rmap based in a later patch, in a
manner which makes it unsafe to be called for a deleted slot, we makes
the caller see if the slot is non-zero and being dirty logged.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 0 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e45c20ca422a..f689a6d7f9d4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -817,7 +817,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
         if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
                 if (kvm_create_dirty_bitmap(&new) < 0)
                         goto out_free;
-                /* destroy any largepage mappings for dirty tracking */
         }
 
         if (!npages || base_gfn != old.base_gfn) {