Re: [PATCH 7/9] vfio/pci: Support mmap() of a VFIO DMABUF

[Jason Gunthorpe]

On Thu, Apr 16, 2026 at 06:17:50AM -0700, Matt Evans wrote:
> +
> +	dma_resv_lock(priv->dmabuf->resv, NULL);
>  	vdev = READ_ONCE(priv->vdev);
>
> +	if (READ_ONCE(priv->revoked) || !vdev) {

Why is this read once? It is inside the resv lock so it is stable?

> +		pr_debug_ratelimited("%s VA 0x%lx, pgoff 0x%lx: DMABUF revoked/cleaned up\n",
> +				     __func__, vmf->address, vma->vm_pgoff);
> +		dma_resv_unlock(priv->dmabuf->resv);
> +		return VM_FAULT_SIGBUS;
> +	}
> +	/* vdev is usable */
> +
> +	if (!vfio_device_try_get_registration(&vdev->vdev)) {
> +		/*
> +		 * If vdev != NULL (above), the registration should
> +		 * already be >0 and so this try_get should never
> +		 * fail.
> +		 */
> +		dev_warn(&vdev->pdev->dev, "%s: Unexpected registration failure\n",
> +			 __func__);
> +		dma_resv_unlock(priv->dmabuf->resv);
> +		return VM_FAULT_SIGBUS;
> +	}
> +	dma_resv_unlock(priv->dmabuf->resv);
> +
>  	scoped_guard(rwsem_read, &vdev->memory_lock) {
> -		if (!priv->revoked) {
> +		if (!READ_ONCE(priv->revoked)) {

Same here, it is not read once since you hold the memory_lock it is
stable.

Jason