On Fri, Sep 19, 2025 at 08:33:23AM +0100, Will Deacon wrote:

pieces and will need to work on the userspace side. It's not like
MSI_IOVA2 is magically going to work (and I bet it won't be tested).

It could, if someone checks the default memory map a second constant
could be selected that works.

quoted

Nicolin has some patches on the iommufd side to let userspace select
the MSI address instead, but they are not done yet.

Maybe we should just wait for that? Carrying a temporary hack with ABI
implications to support broken hardware isn't particularly compelling
to me.

This patch would still be needed for kernel users.

Arguably the kernel users should just be using the iova allocator from
dma-iommu.c. This whole hard coded constant/sneaky uapi is just a hack
to make vfio work..

So maybe if the single constant doesn't work we could set some
indication that the caller must allocate the MSI iova, the kernel can
use the dma-iommu allocator and VFIO can just refuse to use the device
for now.

Jason