Comment 0 for bug 1907421

Description: vfio: pass DMA availability information to userspace
Symptom: vfio-pci device on s390 enters error state
Problem: Commit 492855939bdb added a limit to the number of concurrent
               DMA requests for a vfio container. However, lazy unmapping in
               s390 can in fact cause quite a large number of outstanding DMA
               requests to build up prior to being purged, potentially the
               entire guest DMA space. This results in unexpected errors seen
               in qemu such as 'VFIO_MAP_DMA failed: No space left on device'
Solution: The solution requires a change to both kernel and qemu - For
               the kernel, add the ability to provide the number of allowable
               DMA requests via the VFIO_IOMMU_GET_INFO ioctl.
Reproduction: Put a vfio-pci device on s390 under I/O load
Upstream-ID: a717072007e8aedd3f951726d8cf55454860b30d
               7d6e1329652ed971d1b6e0e7bea66fba5044e271

Need also to be integrated into 20.10 and 20.04.

OK, just to clarify we don't need to fix bionic for this one, but rather focal (20.04) and groovy (20.10). Furthermore, for 20.04, 20.10 and 21.04 ONLY commit 7d6e1329652ed971d1b6e0e7bea66fba5044e271 is needed, the other was a pre-req that is already present.