[PATCH 15/26] vfio/pci: Change the DMA-buf exporter to use mapping_type

[Alistair Popple <apopple@nvidia.com>]

From: Jason Gunthorpe <jgg@nvidia.com>

Simple conversion to add a match_mapping() callback that offers an
exporter SGT mapping type. Later patches will add a physical address
exporter so go straight to adding the match_mapping() function.

The check for attachment->peer2peer is replaced with setting
exporter_requires_p2p=true. VFIO always uses MMIO memory.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
[ dma_buf_mapping_attach() calls ->match_mapping() without
  holding the dma_resv lock, so the dma_resv_assert_held() in
  vfio_pci_dma_buf_match_mapping() fires under lockdep and the priv->vdev
  read it guarded was not serialised against vfio_pci_dma_buf_cleanup()
  either. Fixed as Jason proposed in
  https://lore.kernel.org/all/20260413130147.GG2588311@nvidia.com/: hold a
  pci_dev reference for the lifetime of the dmabuf and use it for the P2P
  match instead of dereferencing priv->vdev. - apopple ]
Reported-by: Baolu Lu <baolu.lu@linux.intel.com>
Closes: https://lore.kernel.org/all/f4e2171a-da58-488f-be02-26a39b5afbe3@linux.intel.com/
Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 drivers/vfio/pci/vfio_pci_dmabuf.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index c16f460c01d6..58e771309c5f 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -12,6 +12,7 @@ MODULE_IMPORT_NS("DMA_BUF");
 struct vfio_pci_dma_buf {
 	struct dma_buf *dmabuf;
 	struct vfio_pci_core_device *vdev;
+	struct pci_dev *pdev;
 	struct list_head dmabufs_elm;
 	size_t size;
 	struct phys_vec *phys_vec;
@@ -27,9 +28,6 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
 {
 	struct vfio_pci_dma_buf *priv = dmabuf->priv;
 
-	if (!attachment->peer2peer)
-		return -EOPNOTSUPP;
-
 	if (priv->revoked)
 		return -ENODEV;
 
@@ -95,15 +93,31 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
 		up_write(&priv->vdev->memory_lock);
 		vfio_device_put_registration(&priv->vdev->vdev);
 	}
+	pci_dev_put(priv->pdev);
 	kfree(priv->phys_vec);
 	kfree(priv);
 }
 
-static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
-	.attach = vfio_pci_dma_buf_attach,
+static const struct dma_buf_mapping_sgt_exp_ops vfio_pci_dma_buf_sgt_ops = {
 	.map_dma_buf = vfio_pci_dma_buf_map,
 	.unmap_dma_buf = vfio_pci_dma_buf_unmap,
+};
+
+static int vfio_pci_dma_buf_match_mapping(struct dma_buf_match_args *args)
+{
+	struct vfio_pci_dma_buf *priv = args->dmabuf->priv;
+	struct dma_buf_mapping_match sgt_match[1];
+
+	sgt_match[0] = DMA_BUF_EMAPPING_SGT_P2P(&vfio_pci_dma_buf_sgt_ops,
+						priv->pdev);
+
+	return dma_buf_match_mapping(args, sgt_match, ARRAY_SIZE(sgt_match));
+}
+
+static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
+	.attach = vfio_pci_dma_buf_attach,
 	.release = vfio_pci_dma_buf_release,
+	.match_mapping = vfio_pci_dma_buf_match_mapping,
 };
 
 /*
@@ -300,6 +314,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 		goto err_dev_put;
 	}
 
+	priv->pdev = pci_dev_get(vdev->pdev);
 	kref_init(&priv->kref);
 	init_completion(&priv->comp);
 
-- 
2.54.0