Novell XEN - ADMINISTRATION Manual page 31

kernel: PCI-DMA: Out of SW-IOMMU space for 32768 bytes at device
000:01:02.0
In this case you need to increase the size of the swiotlb. Add "swiotlb=128" on
the Domain0 cmdline. Note that the number can be adjusted up or down to find
the optimal size for the machine.
Setting Up Virtual Machines 25