Re: [PATCH v3 5/9] vfio/pci: Provide a user-facing name for BAR mappings

[Pranjal Shrivastava <praan@google.com>]

On Wed, Jun 10, 2026 at 04:43:19PM +0100, Matt Evans 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>
> ---
>  drivers/vfio/pci/vfio_pci_dmabuf.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index 2fd3629789bf..8f7f1b909b94 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>
>  
>  #include "vfio_pci_priv.h"
>  
> @@ -470,6 +471,7 @@ 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);
> @@ -482,6 +484,20 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
>  		goto err_free_priv;
>  	}
>  
> +	bufname = kzalloc(DMA_BUF_NAME_LEN, GFP_KERNEL);
> +	if (!bufname) {
> +		ret = -ENOMEM;
> +		goto err_free_phys;
> +	}
> +
> +	/*
> +	 * Maximum size of the friendly debug name is
> +	 * vfio1234567890:ffff:ff:3f.7/5 = 30, which fits within
> +	 * DMA_BUF_NAME_LEN.
> +	 */
> +	snprintf(bufname, DMA_BUF_NAME_LEN, "%s:%s/%x",
> +		 dev_name(&vdev->vdev.device), pci_name(vdev->pdev), res_index);
> +

Nit: Could we instead use:

	bufname = kasprintf(GFP_KERNEL, "%s:%s/%x",
	                    dev_name(&vdev->vdev.device), pci_name(vdev->pdev), res_index);
	if (!bufname)
	    ret = -ENOMEM;
	    [...]

>  	/*
>  	 * The DMABUF begins from the mmap()'s BAR offset, i.e. the
>  	 * start of the VMA corresponds to byte 0 of the DMABUF and
> @@ -500,7 +516,7 @@ 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);
> @@ -508,7 +524,7 @@ 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
> @@ -523,8 +539,15 @@ 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);
> +
>  	return 0;
>  
> +err_free_name:
> +	kfree(bufname);
>  err_free_phys:
>  	kfree(priv->phys_vec);
>  err_free_priv:

Apart from that,

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan