On Wed, Oct 29, 2025 at 05:25:03PM -0700, Samiullah Khawaja wrote:

On Mon, Oct 13, 2025 at 8:27 AM Leon Romanovsky leon@kernel.org wrote:

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From: Leon Romanovsky leonro@nvidia.com

Add support for exporting PCI device MMIO regions through dma-buf, enabling safe sharing of non-struct page memory with controlled lifetime management. This allows RDMA and other subsystems to import dma-buf FDs and build them into memory regions for PCI P2P operations.

The implementation provides a revocable attachment mechanism using dma-buf move operations. MMIO regions are normally pinned as BARs don't change physical addresses, but access is revoked when the VFIO device is closed or a PCI reset is issued. This ensures kernel self-defense against potentially hostile userspace.

Signed-off-by: Jason Gunthorpe jgg@nvidia.com Signed-off-by: Vivek Kasireddy vivek.kasireddy@intel.com Signed-off-by: Leon Romanovsky leonro@nvidia.com

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drivers/vfio/pci/Kconfig | 3 + drivers/vfio/pci/Makefile | 2 + drivers/vfio/pci/vfio_pci_config.c | 22 +- drivers/vfio/pci/vfio_pci_core.c | 28 ++ drivers/vfio/pci/vfio_pci_dmabuf.c | 446 +++++++++++++++++++++++++++++ drivers/vfio/pci/vfio_pci_priv.h | 23 ++ include/linux/vfio_pci_core.h | 1 + include/uapi/linux/vfio.h | 25 ++ 8 files changed, 546 insertions(+), 4 deletions(-) create mode 100644 drivers/vfio/pci/vfio_pci_dmabuf.c

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+void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked) +{

•   struct vfio_pci_dma_buf *priv;
  

•   struct vfio_pci_dma_buf *tmp;
  

•   lockdep_assert_held_write(&vdev->memory_lock);
  

•   list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
  

•           if (!get_file_active(&priv->dmabuf->file))
  

•                   continue;
  

•           if (priv->revoked != revoked) {
  

•                   dma_resv_lock(priv->dmabuf->resv, NULL);
  

•                   priv->revoked = revoked;
  

•                   dma_buf_move_notify(priv->dmabuf);
  

I think this should only be called when revoked is true, otherwise this will be calling move_notify on the already revoked dmabuf attachments.

This case is protected by "if (priv->revoked)" check both in vfio_pci_dma_buf_map and vfio_pci_dma_buf_attach. They will prevent DMABUF recreation if revoked is false.

VTW, please trim your replies, it is time consuming to find your reply among 600 lines of unrelated text.

Thanks

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•                   dma_resv_unlock(priv->dmabuf->resv);
  

•           }
  

•           dma_buf_put(priv->dmabuf);
  

•   }
  

+}