linux-kernel - [PATCH rdma-next 2/2] RDMA/mlx5: Implement DMABUF export ops

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Message-ID: <20260108-dmabuf-export-v1-2-6d47d46580d3@nvidia.com>
Date: Thu, 8 Jan 2026 13:11:15 +0200
From: Edward Srouji <edwards@...dia.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>, "Sumit
 Semwal" <sumit.semwal@...aro.org>, Christian König
	<christian.koenig@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<linaro-mm-sig@...ts.linaro.org>, Yishai Hadas <yishaih@...dia.com>, "Edward
 Srouji" <edwards@...dia.com>
Subject: [PATCH rdma-next 2/2] RDMA/mlx5: Implement DMABUF export ops

From: Yishai Hadas <yishaih@...dia.com>

Enable p2pdma on the mlx5 PCI device to allow DMABUF-based peer-to-peer
DMA mappings.

Add implementation of the mmap_get_pfns and pgoff_to_mmap_entry device
operations required for DMABUF support in the mlx5 RDMA driver.

The pgoff_to_mmap_entry operation converts a page offset to the
corresponding rdma_user_mmap_entry by extracting the command and index
from the offset and looking it up in the ucontext's mmap_xa.

The mmap_get_pfns operation retrieves the physical address and length
from the mmap entry and obtains the p2pdma provider for the underlying
PCI device, which is needed for peer-to-peer DMA operations with
DMABUFs.

Signed-off-by: Yishai Hadas <yishaih@...dia.com>
Signed-off-by: Edward Srouji <edwards@...dia.com>
---
 drivers/infiniband/hw/mlx5/main.c | 72 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index e81080622283..f97c86c96d83 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -2446,6 +2446,70 @@ static int mlx5_ib_mmap_clock_info_page(struct mlx5_ib_dev *dev,
 			      virt_to_page(dev->mdev->clock_info));
 }
 
+static int phys_addr_to_bar(struct pci_dev *pdev, phys_addr_t pa)
+{
+	resource_size_t start, end;
+	int bar;
+
+	for (bar = 0; bar < PCI_STD_NUM_BARS; bar++) {
+		/* Skip BARs not present or not memory-mapped */
+		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
+			continue;
+
+		start = pci_resource_start(pdev, bar);
+		end = pci_resource_end(pdev, bar);
+
+		if (!start || !end)
+			continue;
+
+		if (pa >= start && pa <= end)
+			return bar;
+	}
+
+	return -1;
+}
+
+static int mlx5_ib_mmap_get_pfns(struct rdma_user_mmap_entry *entry,
+				 struct dma_buf_phys_vec *phys_vec,
+				 struct p2pdma_provider **provider)
+{
+	struct mlx5_user_mmap_entry *mentry = to_mmmap(entry);
+	struct pci_dev *pdev = to_mdev(entry->ucontext->device)->mdev->pdev;
+	int bar;
+
+	phys_vec->paddr = mentry->address;
+	phys_vec->len = entry->npages * PAGE_SIZE;
+
+	bar = phys_addr_to_bar(pdev, phys_vec->paddr);
+	if (bar < 0)
+		return -EINVAL;
+
+	*provider = pcim_p2pdma_provider(pdev, bar);
+	/* If the kernel was not compiled with CONFIG_PCI_P2PDMA the
+	 * functionality is not supported.
+	 */
+	if (!*provider)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
+static struct rdma_user_mmap_entry *
+mlx5_ib_pgoff_to_mmap_entry(struct ib_ucontext *ucontext, off_t pg_off)
+{
+	unsigned long entry_pgoff;
+	unsigned long idx;
+	u8 command;
+
+	pg_off = pg_off >> PAGE_SHIFT;
+	command = get_command(pg_off);
+	idx = get_extended_index(pg_off);
+
+	entry_pgoff = command << 16 | idx;
+
+	return rdma_user_mmap_entry_get_pgoff(ucontext, entry_pgoff);
+}
+
 static void mlx5_ib_mmap_free(struct rdma_user_mmap_entry *entry)
 {
 	struct mlx5_user_mmap_entry *mentry = to_mmmap(entry);
@@ -4360,7 +4424,13 @@ static int mlx5_ib_stage_init_init(struct mlx5_ib_dev *dev)
 	if (err)
 		goto err_mp;
 
+	err = pcim_p2pdma_init(mdev->pdev);
+	if (err && err != -EOPNOTSUPP)
+		goto err_dd;
+
 	return 0;
+err_dd:
+	mlx5_ib_data_direct_cleanup(dev);
 err_mp:
 	mlx5_ib_cleanup_multiport_master(dev);
 err:
@@ -4412,11 +4482,13 @@ static const struct ib_device_ops mlx5_ib_dev_ops = {
 	.map_mr_sg_pi = mlx5_ib_map_mr_sg_pi,
 	.mmap = mlx5_ib_mmap,
 	.mmap_free = mlx5_ib_mmap_free,
+	.mmap_get_pfns = mlx5_ib_mmap_get_pfns,
 	.modify_cq = mlx5_ib_modify_cq,
 	.modify_device = mlx5_ib_modify_device,
 	.modify_port = mlx5_ib_modify_port,
 	.modify_qp = mlx5_ib_modify_qp,
 	.modify_srq = mlx5_ib_modify_srq,
+	.pgoff_to_mmap_entry = mlx5_ib_pgoff_to_mmap_entry,
 	.pre_destroy_cq = mlx5_ib_pre_destroy_cq,
 	.poll_cq = mlx5_ib_poll_cq,
 	.post_destroy_cq = mlx5_ib_post_destroy_cq,

-- 
2.49.0