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Message-ID: <c725798d-48da-2993-cc48-0ec0b314455f@linux.dev>
Date: Mon, 31 Jan 2022 11:56:36 -0700
From: Jonathan Derrick <jonathan.derrick@...ux.dev>
To: Logan Gunthorpe <logang@...tatee.com>,
linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
linux-mm@...ck.org, iommu@...ts.linux-foundation.org
Cc: Stephen Bates <sbates@...thlin.com>,
Christoph Hellwig <hch@....de>,
Dan Williams <dan.j.williams@...el.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Christian König <christian.koenig@....com>,
John Hubbard <jhubbard@...dia.com>,
Don Dutile <ddutile@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Jakowski Andrzej <andrzej.jakowski@...el.com>,
Minturn Dave B <dave.b.minturn@...el.com>,
Jason Ekstrand <jason@...kstrand.net>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Xiong Jianxin <jianxin.xiong@...el.com>,
Bjorn Helgaas <helgaas@...nel.org>,
Ira Weiny <ira.weiny@...el.com>,
Robin Murphy <robin.murphy@....com>,
Martin Oliveira <martin.oliveira@...eticom.com>,
Chaitanya Kulkarni <ckulkarnilinux@...il.com>,
Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH v5 00/24] Userspace P2PDMA with O_DIRECT NVMe devices
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@deltatee.com/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
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