Re: [PATCH v4 00/12] VIRTIO-IOMMU/VFIO: Don't assume 64b IOVA space

[Cédric Le Goater]

On 10/19/23 15:45, Eric Auger wrote:
> On x86, when assigning VFIO-PCI devices protected with virtio-iommu
> we encounter the case where the guest tries to map IOVAs beyond 48b
> whereas the physical VTD IOMMU only supports 48b. This ends up with
> VFIO_MAP_DMA failures at qemu level because at kernel level,
> vfio_iommu_iova_dma_valid() check returns false on vfio_map_do_map().
>
> This is due to the fact the virtio-iommu currently unconditionally
> exposes an IOVA range of 64b through its config input range fields.
>
> This series removes this assumption by retrieving the usable IOVA
> regions through the VFIO_IOMMU_TYPE1_INFO_CAP_IOVA_RANGE UAPI when
> a VFIO device is attached. This info is communicated to the
> virtio-iommu memory region, transformed into the inversed info, ie.
> the host reserved IOVA regions. Then those latter are combined with the
> reserved IOVA regions set though the virtio-iommu reserved-regions
> property. That way, the guest virtio-iommu driver, unchanged, is
> able to probe the whole set of reserved regions and prevent any IOVA
> belonging to those ranges from beeing used, achieving the original goal.
>
> Best Regards
>
> Eric
>
> This series can be found at:
> https://github.com/eauger/qemu/tree/iommu_geometry-v4

Applied to vfio-next.

Thanks,

C.


> History:
> v3 -> v4:
> - removed nr_iovas (Alex) and droppped last patch (Alex)
> - Collected Michael's R-b, Peter's R-b and Yanghang's T-b
>
> v2 -> v3:
> - rebase on top of vfio-next (including iommufd prereq)
> - take into account IOVA range info capability may not be offered by
>    old kernel and use nr_iovas = -1 to encode that [Alex]
> - use GList * everywhere instead of arrays (in the range_inverse_array)
>    with the benefice it sorts ranges retrieved from the kernel which are
>    not garanteed to be sorted. Rework the tests accordingly [Alex]
> - Make sure resv_regions GList is build before the probe() [Jean]
>    per device list is first populated with prop resv regions on
>    IOMMUDevice creation and then rebuilt on set_iova()
> - Add a warning if set_iova builds a valid list after probe was
>    called [Jean]
> - Build host windows on top of IOVA valid ranges if this info can
>    be retrieved from the kernel. As many windows are created as
>    valid ranges
> v1 -> v2:
> - Remove "[PATCH 12/13] virtio-iommu: Resize memory region according
>    to the max iova info" which causes way too much trouble: trigger
>    a coredump in vhost, causes duplication of IOMMU notifiers causing
>    EEXIST vfio_dma_map errors, ... This looks like a bad usage of the
>    memory API so I prefer removing this from this series. So I was
>    also obliged to remove the vfio_find_hostwin() check in the case
>    of an IOMMU.
> - Let range_inverse_array() take low/high args instead of hardcoding
>    0, UINT64_MAX which both complexifies the algo and the tests.
> - Move range function description in header.
> - Check that if set_iova_ranges is called several times, new resv
>    regions are included in previous ones
>
>
> Eric Auger (12):
>    memory: Let ReservedRegion use Range
>    memory: Introduce memory_region_iommu_set_iova_ranges
>    vfio: Collect container iova range info
>    virtio-iommu: Rename reserved_regions into prop_resv_regions
>    range: Make range_compare() public
>    util/reserved-region: Add new ReservedRegion helpers
>    virtio-iommu: Introduce per IOMMUDevice reserved regions
>    range: Introduce range_inverse_array()
>    virtio-iommu: Record whether a probe request has been issued
>    virtio-iommu: Implement set_iova_ranges() callback
>    virtio-iommu: Consolidate host reserved regions and property set ones
>    test: Add some tests for range and resv-mem helpers
>
>   include/exec/memory.h            |  34 +++-
>   include/hw/vfio/vfio-common.h    |   1 +
>   include/hw/virtio/virtio-iommu.h |   7 +-
>   include/qemu/range.h             |  14 ++
>   include/qemu/reserved-region.h   |  32 ++++
>   hw/core/qdev-properties-system.c |   9 +-
>   hw/vfio/common.c                 |   9 +
>   hw/vfio/container.c              |  42 +++-
>   hw/virtio/virtio-iommu-pci.c     |   8 +-
>   hw/virtio/virtio-iommu.c         | 155 +++++++++++++--
>   system/memory.c                  |  13 ++
>   tests/unit/test-resv-mem.c       | 318 +++++++++++++++++++++++++++++++
>   util/range.c                     |  61 +++++-
>   util/reserved-region.c           |  91 +++++++++
>   hw/virtio/trace-events           |   1 +
>   tests/unit/meson.build           |   1 +
>   util/meson.build                 |   1 +
>   17 files changed, 764 insertions(+), 33 deletions(-)
>   create mode 100644 include/qemu/reserved-region.h
>   create mode 100644 tests/unit/test-resv-mem.c
>   create mode 100644 util/reserved-region.c