use exact allocation for dma coherent memory

[Jason Gunthorpe]

On Mon, Jun 17, 2019 at 10:33:42AM +0200, Christoph Hellwig wrote:
> > drivers/infiniband/hw/cxgb4/qp.c
> >    129  static int alloc_host_sq(struct c4iw_rdev *rdev, struct t4_sq *sq)
> >    130  {
> >    131          sq->queue = dma_alloc_coherent(&(rdev->lldi.pdev->dev), sq->memsize,
> >    132                                         &(sq->dma_addr), GFP_KERNEL);
> >    133          if (!sq->queue)
> >    134                  return -ENOMEM;
> >    135          sq->phys_addr = virt_to_phys(sq->queue);
> >    136          dma_unmap_addr_set(sq, mapping, sq->dma_addr);
> >    137          return 0;
> >    138  }
> > 
> > Is this a bug?
> 
> Yes.  This will blow up badly on many platforms, as sq->queue
> might be vmapped, ioremapped, come from a pool without page backing.

Gah, this addr gets fed into io_remap_pfn_range/remap_pfn_range too..

Potnuri, you should fix this.. 

You probably need to use dma_mmap_from_dev_coherent() in the mmap ?

Jason