Hi Jason, Will, On 19 Sep 2025 09:08, Jason Gunthorpe wrote: > 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. > > > > 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.
So, are we settling on having two predefined MSI IOVA base constants, and if both of those conflict with reserved regions on a given platform, falling back to dynamic allocation via the IOVA allocator? Just checking if that's the consensus we're reaching. Thanks, Shyam
