[RFC 0/3] NVMe passthrough: Take into account host IOVA reserved regions

[Eric Auger <eric.auger@redhat.com>]

The current IOVA allocator allocates within the [0x10000, 1ULL << 39]
window, without paying attention to the host IOVA reserved regions.
This prevents NVMe passthtrough from working on ARM as the fixed
IOVAs rapidly grow up to the MSI reserved region [0x8000000, 0x8100000]
causing some VFIO MAP DMA failures. This series collects the usable
IOVA regions using VFIO GET_INFO (this requires the host to support
VFIO_IOMMU_TYPE1_INFO_CAP_IOVA_RANGE) and rework the fixed and
temporary IOVA allocators to avoid those latter. Also the min/max
IOVAs now can be dynamically determined.

Unfortunately the usable host IOVA ranges reported by the kernel
currently do not take into account the dma_mask of devices within
the group. This needs to be fixed, otherwise this series might try
to allocate temporary IOVAs within the range supported by the IOMMU
but beyond the allowed dma_mask. I got the case where the SMMU
supports up to 48 bits but the dma_mask only is 42bits. This kernel
dependency plus the testing limited to one peculiar ARM platform
explains the RFC state.

Best Regards

Eric

This series can be found at:
https://github.com/eauger/qemu/tree/nvme_rfc

This was tested on ARM only.


Eric Auger (3):
  util/vfio-helpers: Collect IOVA reserved regions
  util/vfio-helpers: Dynamically compute the min/max IOVA
  util/vfio-helpers: Rework the IOVA allocator to avoid IOVA reserved
    regions

 util/vfio-helpers.c | 162 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 143 insertions(+), 19 deletions(-)

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2.21.3