Re: [PATCH 0/3] Fix virtio-blk issue with SWIOTLB

[Joerg Roedel]

Hi Christoph,

On Thu, Jan 10, 2019 at 02:59:52PM +0100, Christoph Hellwig wrote:
> On Thu, Jan 10, 2019 at 02:44:30PM +0100, Joerg Roedel wrote:

> > The problem is a limitation of the SWIOTLB implementation,
> > which does not support allocations larger than 256kb. When
> > the virtio-blk driver tries to read/write a block larger
> > than that, the allocation of the dma-handle fails and an IO
> > error is reported.
> 
> s/allocations/mappings/, right?  We don't use the swiotlb
> buffer for the coherent allocations anymore, and I don't think
> virtio-blk uses them anyway.

'Allocation' in the sense that there are address ranges allocated, not
memory, but mappings would also be right.

> I really don't like the fact that we hardcode swiotlb specific.
> This needs to be indirect through the dma ops or struct device,
> as various iommu implementations also have limits (although
> usually much larger ones).

I though about exposing it through DMA-API, but didn't go that route as
I didn't want to extend a generic API for some SWIOTLB specifics. But if
there are more implementations that have a size limitation it makes
certainly sense to put it into the DMA-API. I'll change that in the
next version.

Thanks,

	Joerg