linux-kernel - Re: [PATCH 3/4] vdpa: get_iova_range() is mandatory for device specific DMA translation

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Message-ID: <20200805085217-mutt-send-email-mst@kernel.org>
Date:   Wed, 5 Aug 2020 08:55:27 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, rob.miller@...adcom.com,
        lingshan.zhu@...el.com, eperezma@...hat.com, lulu@...hat.com,
        shahafs@...lanox.com, hanand@...inx.com, mhabets@...arflare.com,
        gdawar@...inx.com, saugatm@...inx.com, vmireyno@...vell.com,
        zhangweining@...jie.com.cn, eli@...lanox.com
Subject: Re: [PATCH 3/4] vdpa: get_iova_range() is mandatory for device
 specific DMA translation

On Wed, Jun 17, 2020 at 11:29:46AM +0800, Jason Wang wrote:
> In order to let userspace work correctly, get_iova_range() is a must
> for the device that has its own DMA translation logic.

I guess you mean for a device.

However in absence of ths op, I don't see what is wrong with just
assuming device can access any address.

> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/vdpa/vdpa.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index de211ef3738c..ab7af978ef70 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -82,6 +82,10 @@ struct vdpa_device *__vdpa_alloc_device(struct device *parent,
>  	if (!!config->dma_map != !!config->dma_unmap)
>  		goto err;
>  
> +	if ((config->dma_map || config->set_map) &&
> +	    !config->get_iova_range)
> +		goto err;
> +
>  	err = -ENOMEM;
>  	vdev = kzalloc(size, GFP_KERNEL);
>  	if (!vdev)

What about devices using an IOMMU for translation?
IOMMUs generally have a limited IOVA range too, right?



> -- 
> 2.20.1