Re: [PATCH 00/13] VIRTIO-IOMMU/VFIO: Don't assume 64b IOVA space

[Alex Williamson]

On Mon,  4 Sep 2023 10:03:43 +0200
Eric Auger <eric.auger@redhat.com> 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.

Hi Eric,

I don't quite follow this relative to device hotplug.  Are we
manipulating a per-device memory region which is created at device add
time?  Is that memory region actually shared in some cases, for instance
if we have a PCIe-to-PCI bridge aliasing devices on the conventional
side?  Thanks,

Alex

> This series can be found at:
> https://github.com/eauger/qemu/tree/virtio-iommu_geometry_v1
> 
> Eric Auger (13):
>   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
>   virtio-iommu: Introduce per IOMMUDevice reserved regions
>   range: Introduce range_inverse_array()
>   virtio-iommu: Implement set_iova_ranges() callback
>   range: Make range_compare() public
>   util/reserved-region: Add new ReservedRegion helpers
>   virtio-iommu: Consolidate host reserved regions and property set ones
>   test: Add some tests for range and resv-mem helpers
>   virtio-iommu: Resize memory region according to the max iova info
>   vfio: Remove 64-bit IOVA address space assumption
> 
>  include/exec/memory.h            |  30 ++++-
>  include/hw/vfio/vfio-common.h    |   2 +
>  include/hw/virtio/virtio-iommu.h |   7 +-
>  include/qemu/range.h             |   9 ++
>  include/qemu/reserved-region.h   |  32 +++++
>  hw/core/qdev-properties-system.c |   9 +-
>  hw/vfio/common.c                 |  70 ++++++++---
>  hw/virtio/virtio-iommu-pci.c     |   8 +-
>  hw/virtio/virtio-iommu.c         |  85 +++++++++++--
>  softmmu/memory.c                 |  15 +++
>  tests/unit/test-resv-mem.c       | 198 +++++++++++++++++++++++++++++++
>  util/range.c                     |  41 ++++++-
>  util/reserved-region.c           |  94 +++++++++++++++
>  hw/virtio/trace-events           |   1 +
>  tests/unit/meson.build           |   1 +
>  util/meson.build                 |   1 +
>  16 files changed, 562 insertions(+), 41 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
>