KVM: Fix assigned devices circular locking dependency

kvm->slots_lock is outer to kvm->lock, so take slots_lock
in kvm_vm_ioctl_assign_device() before taking kvm->lock,
rather than taking it in kvm_iommu_map_memslots().

Cc: stable@kernel.org
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/iommu.c

@@ -73,14 +73,13 @@ static int kvm_iommu_map_memslots(struct kvm *kvm)
 {
 	int i, r = 0;
 
-	down_read(&kvm->slots_lock);
 	for (i = 0; i < kvm->nmemslots; i++) {
 		r = kvm_iommu_map_pages(kvm, kvm->memslots[i].base_gfn,
 					kvm->memslots[i].npages);
 		if (r)
 			break;
 	}
-	up_read(&kvm->slots_lock);
+
 	return r;
 }
 
@@ -190,12 +189,11 @@ static void kvm_iommu_put_pages(struct kvm *kvm,
 static int kvm_iommu_unmap_memslots(struct kvm *kvm)
 {
 	int i;
-	down_read(&kvm->slots_lock);
+
 	for (i = 0; i < kvm->nmemslots; i++) {
 		kvm_iommu_put_pages(kvm, kvm->memslots[i].base_gfn,
 				    kvm->memslots[i].npages);
 	}
-	up_read(&kvm->slots_lock);
 
 	return 0;
 }