On Wed, Apr 19, 2017 at 01:02:49PM -0600, Logan Gunthorpe wrote: > > > On 19/04/17 12:32 PM, Jason Gunthorpe wrote: > > On Wed, Apr 19, 2017 at 12:01:39PM -0600, Logan Gunthorpe wrote: > > Not entirely, it would have to call through the whole process > > including the arch_p2p_cross_segment().. > > Hmm, yes. Though it's still not clear what, if anything, > arch_p2p_cross_segment would be doing. Sets up the iommu for arches that place a iommu between the pci root port and other pci root ports. > In my experience, if you are going between host bridges, the CPU > address (or PCI address -- I'm not sure which seeing they are the > same on my system) would still work fine Try it with VT-D turned on. It shouldn't work or there is a notable security hole in your platform.. > > const struct dma_map_ops *comp_ops = get_dma_ops(completer); > > const struct dma_map_ops *init_ops = get_dma_ops(initiator); > > So, in this case, what device does the completer point to? The PCI > device or a more specific GPU device? If it's the former, who's > responsible for setting the new dma_ops? Typically the dma_ops are arch > specific but now you'd be adding ones that are tied to hmm or the gpu. Donno, that is for GPU folks to figure out :) But.. it could point to a GPU and the GPU struct device could have a proxy dma_ops like Dan pointed out. > >> I'm not sure I like the name pci_p2p_same_segment. It reads as though > >> it's only checking if the devices are not the same segment. > > > > Well, that is exactly what it is doing. If it succeeds then the caller > > knows the DMA will not flow outside the segment and no iommu setup/etc > > is required. > > It appears to me like it's calculating the DMA address, and the check is > just a side requirement. It reads as though it's only doing the check. pci_p2p_same_segment_get_pa() then? Jason
