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

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Date:   Thu, 6 Aug 2020 11:27:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...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 2020/8/5 下午8:55, Michael S. Tsirkin wrote:
> 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.


It's just for safe, if you want, we can assume any address without this op.


>
>> 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?


See patch 4 which query the IOMMU geometry in this case:

+        iommu_domain_get_attr(v->domain,
+                      DOMAIN_ATTR_GEOMETRY, &geo);
+        range.start = geo.aperture_start;
+        range.end = geo.aperture_end;

Thanks


>
>
>
>> -- 
>> 2.20.1