Re: ib_umem_get and DMA_API_DEBUG question

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Aug 27, 2019 at 11:28:20AM +0300, Gal Pressman wrote:
> On 26/08/2019 17:05, Gal Pressman wrote:
> > Hi all,
> > 
> > Lately I've been seeing DMA-API call traces on our automated testing runs which
> > complain about overlapping mappings of the same cacheline [1].
> > The problem is (most likely) caused due to multiple calls to ibv_reg_mr with the
> > same address, which as a result DMA maps the same physical addresses more than 7
> > (ACTIVE_CACHELINE_MAX_OVERLAP) times.
> 
> BTW, on rare occasions I'm seeing the boundary check in check_sg_segment [1]
> fail as well. I don't have a stable repro for it though.
> 
> Is this a known issue as well? The comment there states it might be a bug in the
> DMA API implementation, but I'm not sure.
> 
> [1] https://elixir.bootlin.com/linux/v5.3-rc3/source/kernel/dma/debug.c#L1230

Maybe we are missing a dma_set_seg_boundary ?

PCI uses low defaults:

	dma_set_max_seg_size(&dev->dev, 65536);
	dma_set_seg_boundary(&dev->dev, 0xffffffff);

Jason