Hi Logan, On 1/27/2022 5:25 PM, Logan Gunthorpe wrote:
Hi, This patchset continues my work to add userspace P2PDMA access using O_DIRECT NVMe devices. This posting fixes a lot of issues that were addresed in the last posting, which is here[1]. The patchset is rebased onto v5.17-rc1 as well as a rebased version of Ralph Campbell's patches to drop the ZONE_DEVICE page ref count offset. My understanding is this patch has some problems that are yet to be resolved but this will be the direction taken going forward and is included here to show that it is compatible with this patchset. 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 16, then Patches 17 through 21 wire this flag up based on whether the block queue indicates P2PDMA support. Patches 22 through 24 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 patches 3 to 16 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).
Am I understanding that an IO may use a mix of p2pdma and system pages? Would that cause inconsistent latencies?
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 v5.17-rc1. A git branch is available here: https://github.com/sbates130272/linux-p2pmem/ p2pdma_user_cmb_v5 Thanks, Logan [1] https://lore.kernel.org/all/20211117215410.3695-1-logang@xxxxxxxxxxxx/T/#u -- Changes since v4: - Rebase onto v5.17-rc1. - Included Ralph Cambell's patches which removes the ZONE_DEVICE page reference count offset. This is just to demonstrate that this series is compatible with that direction. - Added a comment in pci_p2pdma_map_sg_attrs(), per Chaitanya and included his Reviewed-by tags. - Patch 1 in the last series which cleaned up scatterlist.h has been upstreamed. - Dropped NEED_SG_DMA_BUS_ADDR_FLAG seeing depends on doesn't work with selected symbols, per Christoph. - Switched iov_iter_get_pages_[alloc_]flags to be exported with EXPORT_SYMBOL_GPL, per Christoph. - Renamed zone_device_pages_are_mergeable() to zone_device_pages_have_same_pgmap(), per Christoph. - Renamed .mmap_file_open operation in nvme_ctrl_ops to cdev_file_open(), per Christoph. Changes since v3: - Add some comment and commit message cleanups I had missed for v3, also moved the prototypes for some of the p2pdma helpers to dma-map-ops.h (which I missed in v3 and was suggested in v2). - Add separate cleanup patch for scatterlist.h and change the macros to functions. (Suggested by Chaitanya and Jason, respectively) - Rename sg_dma_mark_pci_p2pdma() and sg_is_dma_pci_p2pdma() to sg_dma_mark_bus_address() and sg_is_dma_bus_address() which is a more generic name (As requested by Jason) - Fixes to some comments and commit messages as suggested by Bjorn and Jason. - Ensure swiotlb is not used with P2PDMA pages. (Per Jason) - The sgtable coversion in RDMA was split out and sent upstream separately, the new patch is only the removal. (Per Jason) - Moved the FOLL_PCI_P2PDMA check outside of get_dev_pagemap() as Jason suggested this will be removed in the near term. - Add two patches to ensure that zone device pages with different pgmaps are never merged in the block layer or sg_alloc_append_table_from_pages() (Per Jason) - Ensure synchronize_rcu() or call_rcu() is used before returning pages to the genalloc. (Jason pointed out that pages are not gauranteed to be unused in all architectures until at least after an RCU grace period, and that synchronize_rcu() was likely too slow to use in the vma close operation. - Collected Acks and Reviews by Bjorn, Jason and Max. Logan Gunthorpe (22): lib/scatterlist: add flag for indicating P2PDMA segments in an SGL PCI/P2PDMA: Attempt to set map_type if it has not been set PCI/P2PDMA: Expose pci_p2pdma_map_type() PCI/P2PDMA: Introduce helpers for dma_map_sg implementations dma-mapping: allow EREMOTEIO return code for P2PDMA transfers dma-direct: support PCI P2PDMA pages in dma-direct map_sg dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support iommu/dma: support PCI P2PDMA pages in dma-iommu map_sg nvme-pci: check DMA ops when indicating support for PCI P2PDMA nvme-pci: convert to using dma_map_sgtable() RDMA/core: introduce ib_dma_pci_p2p_dma_supported() RDMA/rw: drop pci_p2pdma_[un]map_sg() PCI/P2PDMA: Remove pci_p2pdma_[un]map_sg() mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages iov_iter: introduce iov_iter_get_pages_[alloc_]flags() block: add check when merging zone device pages lib/scatterlist: add check when merging zone device pages block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages() block: set FOLL_PCI_P2PDMA in bio_map_user_iov() mm: use custom page_free for P2PDMA pages PCI/P2PDMA: Introduce pci_mmap_p2pmem() nvme-pci: allow mmaping the CMB in userspace Ralph Campbell (2): ext4/xfs: add page refcount helper mm: remove extra ZONE_DEVICE struct page refcount arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +- block/bio.c | 10 +- block/blk-map.c | 7 +- drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +- drivers/infiniband/core/rw.c | 45 +-- drivers/iommu/dma-iommu.c | 67 +++- drivers/nvme/host/core.c | 18 +- drivers/nvme/host/nvme.h | 4 +- drivers/nvme/host/pci.c | 97 +++--- drivers/nvme/target/rdma.c | 2 +- drivers/pci/Kconfig | 5 + drivers/pci/p2pdma.c | 441 +++++++++++++++++++++---- fs/dax.c | 8 +- fs/ext4/inode.c | 5 +- fs/fuse/dax.c | 4 +- fs/xfs/xfs_file.c | 4 +- include/linux/dax.h | 10 + include/linux/dma-map-ops.h | 76 +++++ include/linux/dma-mapping.h | 5 + include/linux/memremap.h | 7 +- include/linux/mm.h | 68 ++-- include/linux/pci-p2pdma.h | 38 +-- include/linux/scatterlist.h | 44 ++- include/linux/uio.h | 6 + include/rdma/ib_verbs.h | 11 + include/uapi/linux/magic.h | 1 + kernel/dma/direct.c | 43 ++- kernel/dma/direct.h | 7 +- kernel/dma/mapping.c | 22 +- lib/iov_iter.c | 25 +- lib/scatterlist.c | 25 +- lib/test_hmm.c | 2 +- mm/gup.c | 22 +- mm/internal.h | 8 + mm/memcontrol.c | 6 +- mm/memremap.c | 75 ++--- mm/migrate.c | 5 - mm/page_alloc.c | 3 + mm/swap.c | 45 +-- 39 files changed, 904 insertions(+), 371 deletions(-) base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07 -- 2.30.2
