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

[Alex Williamson <alex@shazbot.org>]

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: