[RFC 0/5] GPU Direct RDMA (P2P DMA) for Device Private Pages

[Yonatan Maman <ymaman@nvidia.com>]

From: Yonatan Maman <Ymaman@Nvidia.com>

Based on: Provide a new two step DMA mapping API patchset
https://lore.kernel.org/kvm/20241114170247.GA5813@lst.de/T/#t

This patch series aims to enable Peer-to-Peer (P2P) DMA access in
GPU-centric applications that utilize RDMA and private device pages. This
enhancement reduces data transfer overhead by allowing the GPU to directly
expose device private page data to devices such as NICs, eliminating the
need to traverse system RAM, which is the native method for exposing
device private page data.

To fully support Peer-to-Peer for device private pages, the following
changes are proposed:

`Memory Management (MM)`
 * Leverage struct pagemap_ops to support P2P page operations: This
modification ensures that the GPU can directly map device private pages
for P2P DMA.
 * Utilize hmm_range_fault to support P2P connections for device private
pages (instead of Page fault)

`IB Drivers`
Add TRY_P2P_REQ flag for the hmm_range_fault call: This flag indicates the
need for P2P mapping, enabling IB drivers to efficiently handle P2P DMA
requests.

`Nouveau driver`
Add support for the Nouveau p2p_page callback function: This update
integrates P2P DMA support into the Nouveau driver, allowing it to handle
P2P page operations seamlessly.

`MLX5 Driver`
Utilize NIC Address Translation Service (ATS) for ODP memory, to optimize
DMA P2P for private device pages. Also, when P2P DMA mapping fails due to
inaccessible bridges, the system falls back to standard DMA, which uses host
memory, for the affected PFNs

Yonatan Maman (5):
  mm/hmm: HMM API to enable P2P DMA for device private pages
  nouveau/dmem: HMM P2P DMA for private dev pages
  IB/core: P2P DMA for device private pages
  RDMA/mlx5: Add fallback for P2P DMA errors
  RDMA/mlx5: Enabling ATS for ODP memory

 drivers/gpu/drm/nouveau/nouveau_dmem.c | 110 +++++++++++++++++++++++++
 drivers/infiniband/core/umem_odp.c     |   4 +
 drivers/infiniband/hw/mlx5/mlx5_ib.h   |   6 +-
 drivers/infiniband/hw/mlx5/odp.c       |  24 +++++-
 include/linux/hmm.h                    |   3 +-
 include/linux/memremap.h               |   8 ++
 mm/hmm.c                               |  57 ++++++++++---
 7 files changed, 195 insertions(+), 17 deletions(-)

-- 
2.34.1