[v2,0/3] s390x/pci: Accomodate vfio DMA limiting

Message

Matthew Rosato Sept. 14, 2020, 10:29 p.m. UTC

Kernel commit 492855939bdb added a limit to the number of outstanding DMA
requests for a type1 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 'VFIO_MAP_DMA failed: No space left on device'
conditions seen in QEMU.

This patchset adds support to qemu to retrieve the number of allowable DMA
requests via the VFIO_IOMMU_GET_INFO ioctl.  The patches are separated into
vfio hits which add support for reading in VFIO_IOMMU_GET_INFO capability
chains and getting the per-container dma_avail value, and s390 hits to 
track DMA usage on a per-container basis.

Associated kernel patch:
https://marc.info/?l=kvm&m=160012235303068&w=2

Changes from v2:
- Renamed references of dma_limit to dma_avail based on kernel change as
  the ioctl now reports the amount currently available vs the supposed
  limit.
- Because the ioctl now provides a 'living value' vs the limit, it doesn't
  seem appropriate to put it in the VFIOConatiner structure without
  doing the dma_avail tracking there.  So patch 1 shrinks to vfio helper
  routines to find the capability and leaves vfio_connect_container alone. 
- Subsequently, in patch 2 s390-pci issues its own VFIO_IOMMU_GET_INFO to
  read the dma_avail value and use it.

Matthew Rosato (3):
  vfio: Find DMA available capability
  s390x/pci: Honor DMA limits set by vfio
  vfio: Create shared routine for scanning info capabilities

 hw/s390x/s390-pci-bus.c       | 99 ++++++++++++++++++++++++++++++++++++++++---
 hw/s390x/s390-pci-bus.h       |  9 ++++
 hw/s390x/s390-pci-inst.c      | 29 ++++++++++---
 hw/s390x/s390-pci-inst.h      |  3 ++
 hw/vfio/common.c              | 50 ++++++++++++++++++----
 include/hw/vfio/vfio-common.h |  2 +
 6 files changed, 173 insertions(+), 19 deletions(-)