On 4/7/22 08:46, Logan Gunthorpe wrote: > Hi, > > This patchset continues my work to add userspace P2PDMA access using > O_DIRECT NVMe devices. This posting contains some minor fixes and a > rebase onto v5.18-rc1 which contains cleanup from Christoph around > free_zone_device_page() that helps to enable this patchset. The > previous posting was here[1]. > > The patchset enables userspace P2PDMA by allowing userspace to mmap() > allocated chunks of the CMB. The resulting VMA can be passed only > to O_DIRECT IO on NVMe backed files or block devices. A flag is added > to GUP() in Patch <>, then Patches <> through <> wire this flag up based > on whether the block queue indicates P2PDMA support. Patches <> > through <> enable the CMB to be mapped into userspace by mmaping > the nvme char device. > > This is relatively straightforward, however the one significant > problem is that, presently, pci_p2pdma_map_sg() requires a homogeneous > SGL with all P2PDMA pages or all regular pages. Enhancing GUP to > support enforcing this rule would require a huge hack that I don't > expect would be all that pallatable. So the first 13 patches add > support for P2PDMA pages to dma_map_sg[table]() to the dma-direct > and dma-iommu implementations. Thus systems without an IOMMU plus > Intel and AMD IOMMUs are supported. (Other IOMMU implementations would > then be unsupported, notably ARM and PowerPC but support would be added > when they convert to dma-iommu). > > dma_map_sgtable() is preferred when dealing with P2PDMA memory as it > will return -EREMOTEIO when the DMA device cannot map specific P2PDMA > pages based on the existing rules in calc_map_type_and_dist(). > > The other issue is dma_unmap_sg() needs a flag to determine whether a > given dma_addr_t was mapped regularly or as a PCI bus address. To allow > this, a third flag is added to the page_link field in struct > scatterlist. This effectively means support for P2PDMA will now depend > on CONFIG_64BIT. > > Feedback welcome. > > This series is based on v5.18-rc1. A git branch is available here: > > https://github.com/sbates130272/linux-p2pmem/ p2pdma_user_cmb_v6 > > Thanks, > > Logan > > [1] lkml.kernel.org/r/20220128002614.6136-1-logang@xxxxxxxxxxxx > > -- Do you have any plans to re-spin this ? -ck
