Re: [PATCH WIP 40/43] mlx5: Allocate private context for arbitrary scatterlist registration

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On Wed, Jul 22, 2015 at 11:30:48AM -0600, Jason Gunthorpe wrote:
> On Wed, Jul 22, 2015 at 09:55:40AM +0300, Sagi Grimberg wrote:
> > +	size += max_t(int, MLX5_UMR_ALIGN - ARCH_KMALLOC_MINALIGN, 0);
> > +	mr->klms = kzalloc(size, GFP_KERNEL);
> > +	if (!mr->klms)
> > +		return -ENOMEM;
> > +
> > +	mr->pl_map = dma_map_single(device->dma_device, mr->klms,
> > +				    size, DMA_TO_DEVICE);
> 
> This is a misuse of the DMA API, you must call dma_map_single after
> the memory is set by the CPU, not before.
>
> The fast reg varient is using coherent allocations, which is OK..

It's fine as long as you dma_sync_*_for_{cpu,device} in the right
places, which is what a lot of drivers do for longer held allocations.
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