linux-kernel - Re: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping

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Date:   Tue, 23 Jul 2019 17:38:51 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Eric Auger <eric.auger@...hat.com>, eric.auger.pro@...il.com,
        hch@....de, m.szyprowski@...sung.com, mst@...hat.com,
        jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size
 call

On Mon, Jul 22, 2019 at 04:36:09PM +0100, Robin Murphy wrote:
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index c8be1c4f5b55..37c143971211 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -262,7 +262,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev)
>>   {
>>   	size_t max_segment_size = SIZE_MAX;
>>   -	if (vring_use_dma_api(vdev))
>> +	if (vring_use_dma_api(vdev) && vdev->dev.dma_mask)
>
> Hmm, might it make sense to roll that check up into vring_use_dma_api() 
> itself? After all, if the device has no mask then it's likely that other 
> DMA API ops wouldn't really work as expected either.

Makes sense to me.