[Linaro-mm-sig] Re: [RFC PATCH 4/7] dma-buf: uapi: Mechanism to revoke DMABUFs via ioctl()

On 2/26/26 21:22, Matt Evans wrote:

Add a new dma-buf ioctl() op, DMA_BUF_IOCTL_REVOKE, connected to a new (optional) dma_buf_ops callback, revoke(). An exporter receiving this will _permanently_ revoke the DMABUF, meaning it can no longer be mapped/attached/mmap()ed. It also guarantees that existing importers have been detached (e.g. via move_notify) and all mappings made inaccessible.

This is useful for lifecycle management in scenarios where a process has created a DMABUF representing a resource, then delegated it to a client process; access to the resource is revoked when the client is deemed "done", and the resource can be safely re-used elsewhere.

Well that means revoking from the importer side. That absolutely doesn't make sense to me.

Why would you do that?

Regards, Christian.

Signed-off-by: Matt Evans mattev@meta.com

drivers/dma-buf/dma-buf.c | 5 +++++ include/linux/dma-buf.h | 22 ++++++++++++++++++++++ include/uapi/linux/dma-buf.h | 1 + 3 files changed, 28 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index edaa9e4ee4ae..b9b315317f2d 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -561,6 +561,11 @@ static long dma_buf_ioctl(struct file *file, case DMA_BUF_IOCTL_IMPORT_SYNC_FILE: return dma_buf_import_sync_file(dmabuf, (const void __user *)arg); #endif

•   case DMA_BUF_IOCTL_REVOKE:
  

•           if (dmabuf->ops->revoke)
  

•                   return dmabuf->ops->revoke(dmabuf);
  

•           else
  

•                   return -EINVAL;
  
    default:
            return -ENOTTY;
  

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 0bc492090237..a68c9ad7aebd 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -277,6 +277,28 @@ struct dma_buf_ops {

    int (*vmap)(struct dma_buf *dmabuf, struct iosys_map *map);
    void (*vunmap)(struct dma_buf *dmabuf, struct iosys_map *map);

•   /**
  

•    * @revoke:
  

•    *
  

•    * This callback is invoked from a userspace
  

•    * DMA_BUF_IOCTL_REVOKE operation, and requests that access to
  

•    * the buffer is immediately and permanently revoked.  On
  

•    * successful return, the buffer is not accessible through any
  

•    * mmap() or dma-buf import.  The request fails if the buffer
  

•    * is pinned; otherwise, the exporter marks the buffer as
  

•    * inaccessible and uses the move_notify callback to inform
  

•    * importers of the change.  The buffer is permanently
  

•    * disabled, and the exporter must refuse all map, mmap,
  

•    * attach, etc. requests.
  

•    *
  

•    * Returns:
  

•    *
  

•    * 0 on success, or a negative error code on failure:
  

•    * -ENODEV if the associated device no longer exists/is closed.
  

•    * -EBADFD if the buffer has already been revoked.
  

•    */
  

•   int (*revoke)(struct dma_buf *dmabuf);
  

};

/** diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index 5a6fda66d9ad..84bf2dd2d0f3 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -178,5 +178,6 @@ struct dma_buf_import_sync_file { #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, __u64) #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file) #define DMA_BUF_IOCTL_IMPORT_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file) +#define DMA_BUF_IOCTL_REVOKE _IO(DMA_BUF_BASE, 4)

#endif

2.47.3