kvm: iommu: Add cond_resched to legacy device assignment code

When assigning devices to large memory guests (>=128GB guest
memory in the failure case) the functions to create the
IOMMU page-tables for the whole guest might run for a very
long time. On non-preemptible kernels this might cause
Soft-Lockup warnings. Fix these by adding a cond_resched()
to the mapping and unmapping loops.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/iommu.c

@@ -138,7 +138,7 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
 
 		gfn += page_size >> PAGE_SHIFT;
 
-
+		cond_resched();
 	}
 
 	return 0;
@@ -306,6 +306,8 @@ static void kvm_iommu_put_pages(struct kvm *kvm,
 		kvm_unpin_pages(kvm, pfn, unmap_pages);
 
 		gfn += unmap_pages;
+
+		cond_resched();
 	}
 }