linux-kernel - [PATCH v4 0/2] block: Enable proper MMIO memory handling for P2P DMA

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Message-ID: <20251112-block-with-mmio-v4-0-54aeb609d28d@nvidia.com>
Date: Wed, 12 Nov 2025 21:48:03 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Jens Axboe <axboe@...nel.dk>,
	Keith Busch <kbusch@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-nvme@...ts.infradead.org
Subject: [PATCH v4 0/2] block: Enable proper MMIO memory handling for P2P DMA

Changelog:
v4:
 * Changed double "if" to be "else if".
 * Added missed PCI_P2PDMA_MAP_NONE case.
v3: https://patch.msgid.link/20251027-block-with-mmio-v3-0-ac3370e1f7b7@nvidia.com
 * Encoded p2p map type in IOD flags instead of DMA attributes.
 * Removed REQ_P2PDMA flag from block layer.
 * Simplified map_phys conversion patch.
v2: https://lore.kernel.org/all/20251020-block-with-mmio-v2-0-147e9f93d8d4@nvidia.com/
 * Added Chirstoph's Reviewed-by tag for first patch.
 * Squashed patches
 * Stored DMA MMIO attribute in NVMe IOD flags variable instead of block layer.
v1: https://patch.msgid.link/20251017-block-with-mmio-v1-0-3f486904db5e@nvidia.com
 * Reordered patches.
 * Dropped patch which tried to unify unmap flow.
 * Set MMIO flag separately for data and integrity payloads.
v0: https://lore.kernel.org/all/cover.1760369219.git.leon@kernel.org/

----------------------------------------------------------------------

This patch series improves block layer and NVMe driver support for MMIO
memory regions, particularly for peer-to-peer (P2P) DMA transfers that
go through the host bridge.

The series addresses a critical gap where P2P transfers through the host
bridge (PCI_P2PDMA_MAP_THRU_HOST_BRIDGE) were not properly marked as
MMIO memory, leading to potential issues with:

- Inappropriate CPU cache synchronization operations on MMIO regions
- Incorrect DMA mapping/unmapping that doesn't respect MMIO semantics  
- Missing IOMMU configuration for MMIO memory handling

This work is extracted from the larger DMA physical API improvement
series [1] and focuses specifically on block layer and NVMe requirements
for MMIO memory support.

Thanks

[1] https://lore.kernel.org/all/cover.1757423202.git.leonro@nvidia.com/

---
Leon Romanovsky (2):
      nvme-pci: migrate to dma_map_phys instead of map_page
      block-dma: properly take MMIO path

 block/blk-mq-dma.c            | 19 +++++----
 drivers/nvme/host/pci.c       | 90 +++++++++++++++++++++++++++++++++++--------
 include/linux/bio-integrity.h |  1 -
 include/linux/blk-integrity.h | 14 -------
 include/linux/blk-mq-dma.h    | 28 +++++++-------
 include/linux/blk_types.h     |  2 -
 6 files changed, 99 insertions(+), 55 deletions(-)
---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20251016-block-with-mmio-02acf4285427

Best regards,
--  
Leon Romanovsky <leonro@...dia.com>