On Wed, Jul 10, 2024 at 08:22:12AM +0200, Christoph Hellwig wrote: > On Tue, Jul 09, 2024 at 04:03:20PM -0300, Jason Gunthorpe wrote: > > > Except for the powerpc bypass IOMMU or not is a global decision, > > > and the bypass is per I/O. So I'm not sure what else you want there? > > > > For P2P we know if the DMA will go through the IOMMU or not based on > > the PCIe fabric path between the initiator (the one doing the DMA) and > > the target (the one providing the MMIO memory). > > Oh, yes. So effectively you are asking if we can arbitrarily mix > P2P sources in a single map request. I think the only sane answer > from the iommu/dma subsystem perspective is: hell no. Well, today we can mix them and the dma_map_sg will sort it out. With this new API we can't anymore. So this little detail needs to be taken care of somehow as well, and I didn't see it in this RFC. > For the block layer just having one kind per BIO is fine right now, > although I could see use cases where people would want to combine > them. We can probably defer that until it is needed, though. Do you have an application in mind that would want multi-kind per BIO? Jason
