[PATCH] vfio iommu: Add dma limit capability

[Matthew Rosato]

Commit 492855939bdb ("vfio/type1: Limit DMA mappings per container") 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 'VFIO_MAP_DMA
failed: No space left on device' conditions seen in QEMU.

This patch proposes to provide the DMA limit via the VFIO_IOMMU_GET_INFO
ioctl as a new capability.  A subsequent patchset to QEMU would collect
this information and use it in s390 PCI support to tap the guest on the
shoulder before overrunning the vfio limit.

Matthew Rosato (1):
  vfio iommu: Add dma limit capability

 drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
 include/uapi/linux/vfio.h       | 16 ++++++++++++++++
 2 files changed, 33 insertions(+)

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1.8.3.1