Re: [PATCH v2 0/2] VIRTIO-IOMMU/VFIO page size related fixes

[Jean-Philippe Brucker]

On Wed, Jul 05, 2023 at 06:51:16PM +0200, Eric Auger wrote:
> When assigning a host device and protecting it with the virtio-iommu we may
> end up with qemu crashing with
> 
>     qemu-kvm: virtio-iommu page mask 0xfffffffffffff000 is incompatible
>     with mask 0x20010000
>     qemu: hardware error: vfio: DMA mapping failed, unable to continue
> 
> This happens if the host features a 64kB page size and constraints
> the physical IOMMU to use a 64kB page size. By default 4kB granule is used
> by the qemu virtio-iommu device and this latter becomes aware of the 64kB
> requirement too late, after the machine init, when the vfio device domain is
> attached. virtio_iommu_set_page_size_mask() fails and this causes
> vfio_listener_region_add() to end up with hw_error(). Currently the
> granule is global to all domains.
> 
> To work around this issue, despite the IOMMU MR may be bypassed, we
> transiently enable it on machine init done to get vfio_listener_region_add
> and virtio_iommu_set_page_size_mask called ealier, before the domain
> attach. That way the page size requirement can be taken into account
> before the guest gets started.
> 
> Also get benefit of this series to do some cleanups in some traces
> which may confuse the end user.

For both patches:

Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Tested-by: Jean-Philippe Brucker <jean-philippe@linaro.org>