Ensure that a PCI BAR cannot be registered for native ZONE_DEVICE P2P
if it is already being used as a source for exported DMABUFs.

Add region_index to struct vfio_pci_dma_buf to track the source BAR.
Introduce a new helper function, vfio_pci_bar_is_dmabuf() to scan the
device's active DMABUF list. When a registration request is received via
VFIO_DEVICE_FEATURE_P2P_REGISTER, VFIO rejects the request with -EBUSY
if any active DMABUF originates from the target BAR.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/vfio/pci/vfio_pci_core.c   |  6 ++++++
 drivers/vfio/pci/vfio_pci_dmabuf.c | 16 ++++++++++++++++
 drivers/vfio/pci/vfio_pci_priv.h   |  6 ++++++
 3 files changed, 28 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 9cf494b765e7..7913b8916df9 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1579,6 +1579,12 @@ static int vfio_pci_core_feature_p2p_register(struct vfio_pci_core_device *vdev,
 	if (vdev->p2p_registered_bars & (1 << bar_index))
 		return 0;
 
+	if (vfio_pci_bar_is_dmabuf(vdev, bar_index)) {
+		pci_warn(vdev->pdev, "BAR %d has active DMABUFs. Cannot register for P2P.\n",
+			 bar_index);
+		return -EBUSY;
+	}
+
 	ret = pci_p2pdma_add_resource(vdev->pdev, bar_index, 0, 0);
 	if (ret && ret != -EEXIST)
 		return ret;
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 6635a8681291..194d74724422 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -17,6 +17,7 @@ struct vfio_pci_dma_buf {
 	struct phys_vec *phys_vec;
 	struct p2pdma_provider *provider;
 	u32 nr_ranges;
+	u32 region_index;
 	struct kref kref;
 	struct completion comp;
 	u8 revoked : 1;
@@ -279,6 +280,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 
 	priv->vdev = vdev;
 	priv->nr_ranges = get_dma_buf.nr_ranges;
+	priv->region_index = get_dma_buf.region_index;
 	priv->size = length;
 	ret = vdev->pci_ops->get_dmabuf_phys(vdev, &priv->provider,
 					     get_dma_buf.region_index,
@@ -410,3 +412,17 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
 	}
 	up_write(&vdev->memory_lock);
 }
+
+bool vfio_pci_bar_is_dmabuf(struct vfio_pci_core_device *vdev, int index)
+{
+	struct vfio_pci_dma_buf *priv;
+
+	lockdep_assert_held(&vdev->memory_lock);
+
+	list_for_each_entry(priv, &vdev->dmabufs, dmabufs_elm) {
+		if (priv->region_index == index)
+			return true;
+	}
+	return false;
+}
+EXPORT_SYMBOL_GPL(vfio_pci_bar_is_dmabuf);
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index fca9d0dfac90..0a5da4d5edc4 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -120,6 +120,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 				  size_t argsz);
 void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
 void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
+bool vfio_pci_bar_is_dmabuf(struct vfio_pci_core_device *vdev, int index);
 #else
 static inline int
 vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
@@ -128,6 +129,11 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 {
 	return -ENOTTY;
 }
+static inline bool vfio_pci_bar_is_dmabuf(struct vfio_pci_core_device *vdev,
+					  int index)
+{
+	return false;
+}
 static inline void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
 {
 }
-- 
2.54.0.1099.g489fc7bff1-goog