Re: [PATCH v2 0/3] VIRTIO-IOMMU: Introduce an aw-bits option

[YangHang Liu]

There is no VFIO_MAP_DMA error when hotplug 2 E810 PFs into a VM which
has a virtio-iommu device.

In addition, 21 regression tests of Tier1 level were run and all got PASS.

Tested-by: Yanghang Liu<yanghliu@redhat.com>


On Fri, Feb 2, 2024 at 12:33 AM Eric Auger <eric.auger@redhat.com> wrote:
>
> In [1] and [2] we attempted to fix a case where a VFIO-PCI device
> protected with a virtio-iommu is assigned to an x86 guest. On x86
> the physical IOMMU may have an address width (gaw) of 39 or 48 bits
> whereas the virtio-iommu exposes a 64b input address space by default.
> Hence the guest may try to use the full 64b space and DMA MAP
> failures may be encountered. To work around this issue we endeavoured
> to pass usable host IOVA regions (excluding the out of range space) from
> VFIO to the virtio-iommu device so that the virtio-iommu driver can
> query those latter during the probe request and let the guest iommu
> kernel subsystem carve them out.
>
> However if there are several devices in the same iommu group,
> only the reserved regions of the first one are taken into
> account by the iommu subsystem of the guest. This generally
> works on baremetal because devices are not going to
> expose different reserved regions. However in our case, this
> may prevent from taking into account the host iommu geometry.
>
> So the simplest solution to this problem looks to introduce an
> input address width option, aw-bits, which matches what is
> done on the intel-iommu. By default, from now on it is set
> to 39 bits with pc_q35 and 48 with arm virt. This replaces the
> previous default value of 64b. So we need to introduce a compat
> for machines older than 9.0 to behave similarly. We use
> hw_compat_8_2 to acheive that goal.
>
> Outstanding series [2] remains useful to let resv regions beeing
> communicated on time before the probe request.
>
> [1] [PATCH v4 00/12] VIRTIO-IOMMU/VFIO: Don't assume 64b IOVA space
>     https://lore.kernel.org/all/20231019134651.842175-1-eric.auger@redhat.com/
>     - This is merged -
>
> [2] [RFC 0/7] VIRTIO-IOMMU/VFIO: Fix host iommu geometry handling for 
> hotplugged devices
>     https://lore.kernel.org/all/20240117080414.316890-1-eric.auger@redhat.com/
>     - This is pending for review on the ML -
>
> This series can be found at:
> https://github.com/eauger/qemu/tree/virtio-iommu-aw-bits-v2
>
> Applied on top of [3]
> [PATCH v2] virtio-iommu: Use qemu_real_host_page_mask as default 
> page_size_mask
> https://lore.kernel.org/all/20240117132039.332273-1-eric.auger@redhat.com/
>
> History:
> v1 -> v2
> - Limit aw to 48b on ARM
> - Check aw is within [32,64]
> - Use hw_compat_8_2
>
> Eric Auger (3):
>   virtio-iommu: Add an option to define the input range width
>   virtio-iommu: Trace domain range limits as unsigned int
>   hw: Set virtio-iommu aw-bits default value on pc_q35_9.0 and arm virt
>
>  include/hw/virtio/virtio-iommu.h | 1 +
>  hw/arm/virt.c                    | 6 ++++++
>  hw/core/machine.c                | 5 ++++-
>  hw/i386/pc.c                     | 6 ++++++
>  hw/virtio/virtio-iommu.c         | 7 ++++++-
>  hw/virtio/trace-events           | 2 +-
>  6 files changed, 24 insertions(+), 3 deletions(-)
>
> --
> 2.41.0
>