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

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Date:   Wed, 24 Jul 2019 18:10:53 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>,
        Eric Auger <eric.auger@...hat.com>, eric.auger.pro@...il.com,
        m.szyprowski@...sung.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 Tue, Jul 23, 2019 at 05:38:51PM +0200, Christoph Hellwig wrote:
> 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.

Christoph - would a documented API wrapping dma_mask make sense?
With the documentation explaining how users must
desist from using DMA APIs if that returns false ...


-- 
MST