KVM: x86: Don't call kvm_mmu_change_mmu_pages() if the count hasn't changed

There is no point in calling kvm_mmu_change_mmu_pages() for memslot
operations that don't change the total page count, so do it just for
KVM_MR_CREATE and KVM_MR_DELETE.
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <9e56b7616a11f5654e4ab486b3237366b7ba9f2a.1638817640.git.maciej.szmigiero@oracle.com>

arch/x86/kvm/x86.c

@@ -11783,7 +11783,8 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	if (!kvm->arch.n_requested_mmu_pages)
+	if (!kvm->arch.n_requested_mmu_pages &&
+	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE))
 		kvm_mmu_change_mmu_pages(kvm,
 				kvm_mmu_calculate_default_mmu_pages(kvm));