KVM: set_memory_region: Don't check for overlaps unless we create or move a slot

Don't need the check for deleting an existing slot or just modifiying
the flags.

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, 10 insertions, 8 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 28eb160fd487..fca64879f967 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -782,14 +782,16 @@ int __kvm_set_memory_region(struct kvm *kvm,
         if (!npages && !old.npages)
                 goto out;
 
-        /* Check for overlaps */
-        r = -EEXIST;
-        kvm_for_each_memslot(slot, kvm->memslots) {
-                if (slot->id >= KVM_USER_MEM_SLOTS || slot == memslot)
-                        continue;
-                if (!((base_gfn + npages <= slot->base_gfn) ||
-                      (base_gfn >= slot->base_gfn + slot->npages)))
-                        goto out;
+        if ((npages && !old.npages) || (base_gfn != old.base_gfn)) {
+                /* Check for overlaps */
+                r = -EEXIST;
+                kvm_for_each_memslot(slot, kvm->memslots) {
+                        if (slot->id >= KVM_USER_MEM_SLOTS || slot == memslot)
+                                continue;
+                        if (!((base_gfn + npages <= slot->base_gfn) ||
+                              (base_gfn >= slot->base_gfn + slot->npages)))
+                                goto out;
+                }
         }
 
         /* Free page dirty bitmap if unneeded */