[Linaro-mm-sig] Re: [PATCH v5 6/9] vfio/pci: Provide a user-facing name for BAR mappings

On Wed, 15 Jul 2026 18:47:29 +0100 Matt Evans matt@ozlabs.org wrote:

Since converting BAR mmap()s to using DMABUFs, we lose the original device path in /proc/<pid>/maps, lsof, etc. Generate a debug-oriented synthetic 'filename' based on the cdev, plus BDF, plus resource index.

This applies only to BAR mappings via the VFIO device fd, as explicitly-exported DMABUFs are named by userspace via the DMA_BUF_SET_NAME ioctl.

Signed-off-by: Matt Evans matt@ozlabs.org Reviewed-by: Pranjal Shrivastava praan@google.com

---

drivers/vfio/pci/vfio_pci_dmabuf.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c index 46b3cf5dc94b..51606ff3cdc6 100644 --- a/drivers/vfio/pci/vfio_pci_dmabuf.c +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c @@ -4,6 +4,7 @@ #include <linux/dma-buf-mapping.h> #include <linux/pci-p2pdma.h> #include <linux/dma-resv.h> +#include <uapi/linux/dma-buf.h>

Is this required? It seems unused.

#include "vfio_pci_priv.h" @@ -486,6 +487,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev, { struct vfio_pci_dma_buf *priv; unsigned long vma_pgoff = vma->vm_pgoff & (VFIO_PCI_OFFSET_MASK >> PAGE_SHIFT);

• char *bufname; int ret;

priv = kzalloc_obj(*priv); @@ -498,6 +500,15 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev, goto err_free_priv; }

• bufname = kasprintf(GFP_KERNEL, "%s:%s/%x",

• 	    dev_name(&vdev->vdev.device), pci_name(vdev->pdev),
  

• 	    res_index);
  

• if (!bufname) {

• ret = -ENOMEM;
  

• goto err_free_phys;
  

• }
• /*
  • The DMABUF begins from the mmap()'s BAR offset, i.e. the
  • start of the VMA corresponds to byte 0 of the DMABUF and

@@ -516,7 +527,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev, priv->provider = pcim_p2pdma_provider(vdev->pdev, res_index); if (!priv->provider) { ret = -EINVAL;

• goto err_free_phys;
  

• goto err_free_name;
  

  }

priv->phys_vec[0].paddr = phys_start + ((u64)vma_pgoff << PAGE_SHIFT); @@ -524,7 +535,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev, ret = vfio_pci_dmabuf_export(vdev, priv, O_CLOEXEC | O_RDWR); if (ret)

• goto err_free_phys;
  

• goto err_free_name;
  

/* * Ownership of the DMABUF file transfers to the VMA so that @@ -539,8 +550,15 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev, vma->vm_file = priv->dmabuf->file; vma->vm_private_data = priv;

• spin_lock(&priv->dmabuf->name_lock);
• kfree(priv->dmabuf->name);
• priv->dmabuf->name = bufname;
• spin_unlock(&priv->dmabuf->name_lock);

This is simple, but shouldn't it really have a sanctioned, exported dmabuf helper rather than open coding this handling? Thanks,

Alex

• return 0;

+err_free_name:

• kfree(bufname);

err_free_phys: kfree(priv->phys_vec); err_free_priv: