KVM: mmu_shrink: kvm_mmu_zap_page requires slots_lock to be held

Index: kvm/arch/x86/kvm/mmu.c
===================================================================
@@ -1987,6 +1987,8 @@ static int mmu_shrink(int nr_to_scan, gf
 	list_for_each_entry(kvm, &vm_list, vm_list) {
 		int npages;
 
+		if (!down_read_trylock(&kvm->slots_lock))
+			continue;
 		spin_lock(&kvm->mmu_lock);
 		npages = kvm->arch.n_alloc_mmu_pages -
 			 kvm->arch.n_free_mmu_pages;

@@ -1999,6 +2001,7 @@ static int mmu_shrink(int nr_to_scan, gf
 		nr_to_scan--;
 
 		spin_unlock(&kvm->mmu_lock);
+		up_read(&kvm->slots_lock);
 	}
 	if (kvm_freed)
 		list_move_tail(&kvm_freed->vm_list, &vm_list);