RE: [PATCH v3 4/5] iommufd: Add replace support in iommufd_access_set_ioas()

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Saturday, February 25, 2023 9:52 AM
> 
> +	/*
> +	 * Set ioas to NULL to block any further iommufd_access_pin_pages().
> +	 * iommufd_access_unpin_pages() can continue using access-
> >ioas_unpin.
> +	 */
> +	access->ioas = NULL;
> +
> +	mutex_unlock(&access->ioas_lock);
> +	access->ops->unmap(access->data, 0, ULONG_MAX);
> +	mutex_lock(&access->ioas_lock);

This should check whether @unmap is valid.