[Linaro-mm-sig] Re: [PATCH v8 9/9] vfio/pci: Revoke a DMABUF on request from userspace

On Tue, 6 Oct 2026 20:36:37 +0100 Matt Evans matt@ozlabs.org wrote:

+#ifdef CONFIG_VFIO_PCI_DMABUF +int vfio_pci_core_feature_dma_buf_revoke(

• struct vfio_pci_core_device *vdev, u32 flags,
• struct vfio_device_feature_dma_buf_revoke __user *arg,
• size_t argsz)

+{

• struct vfio_device_feature_dma_buf_revoke db_revoke;
• struct vfio_pci_dma_buf *priv;
• struct dma_buf *dmabuf;
• int ret;
• if (!vdev->pci_ops || !vdev->pci_ops->get_dmabuf_phys)

• return -EOPNOTSUPP;
  

• ret = vfio_check_feature(flags, argsz,

• 		 VFIO_DEVICE_FEATURE_SET,
  

• 		 sizeof(db_revoke));
  

• if (ret != 1)

• return ret;
  

• if (copy_from_user(&db_revoke, arg, sizeof(db_revoke)))

• return -EFAULT;
  

• dmabuf = dma_buf_get(db_revoke.dmabuf_fd);
• if (IS_ERR(dmabuf))

• return PTR_ERR(dmabuf);
  

• priv = dmabuf->priv;
• /*

• * Sanity-check the DMABUF is really a vfio_pci_dma_buf _and_
  

• * relates to the VFIO device it was provided with.
  

• *
  

• * If the DMABUF relates to this vdev then priv->vdev is
  

• * stable because this open fd prevents cleanup.
  

• *
  

• * If it relates to a different vdev, reading priv->vdev might
  

• * race with a concurrent cleanup on that device.  But if so,
  

• * it points to a non-matching vdev or NULL and is unusable
  

• * either way.
  

• */
  

• if (dmabuf->ops != &vfio_pci_dmabuf_ops ||

•    READ_ONCE(priv->vdev) != vdev) {
  

• ret = -ENODEV;
  

• goto out_put_buf;
  

• }
• /*

• * memory_lock(R) is taken to stop vfio_pci_dev_set_hot_reset()
  

• * from getting it and then blocking all devices in the dev_set behind
  

• * this revoke's drain.
  

• */
  

• down_read(&vdev->memory_lock);
• down_write(&vdev->dmabuf_lock);
• if (priv->status == VFIO_PCI_DMABUF_DEAD) {

• ret = -EBADFD;
  

Kind of ugly to special case the condition in the caller that's already tested in the function. Why not return an errno for this purpose? Thanks,

Alex

• } else {

• vfio_pci_dma_buf_set_status(priv, VFIO_PCI_DMABUF_DEAD);
  

• ret = 0;
  

• }
• up_write(&vdev->dmabuf_lock);
• up_read(&vdev->memory_lock);

+out_put_buf:

• dma_buf_put(dmabuf);
• return ret;

+} +#endif /* CONFIG_VFIO_PCI_DMABUF */