Re: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call

From: Christoph Hellwig
Date: Thu Jul 25 2019 - 14:06:20 EST

On Thu, Jul 25, 2019 at 01:53:49PM +0200, Auger Eric wrote:
> I am confused: if vring_use_dma_api() returns false if the dma_mask is
> unset (ie. vring_use_dma_api() returns false), the virtio-blk-pci device
> will not be able to get translated addresses and won't work properly.
> The patch above allows the dma api to be used and only influences the
> max_segment_size and it works properly.
> So is it normal the dma_mask is unset in my case?

Its not normal. I assume you use virtio-nmio? Due to the mess with
the dma_mask being a pointer a lot of subsystems forgot to set a dma
mask up, and oddly enough seem to mostly get away with it.