Re: [PATCH for-next 2/2] RDMA/hns: Fix wrong maximum DMA segment size

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Apr 07, 2025 at 09:51:37PM +0800, Junxian Huang wrote:
> 
> 
> On 2025/4/4 21:27, Jason Gunthorpe wrote:
> > On Wed, Apr 02, 2025 at 12:05:36PM +0800, Junxian Huang wrote:
> >>
> >>
> >> On 2025/4/2 0:39, Jason Gunthorpe wrote:
> >>> On Thu, Mar 27, 2025 at 07:47:24PM +0800, Junxian Huang wrote:
> >>>> @@ -763,7 +763,7 @@ static int hns_roce_register_device(struct hns_roce_dev *hr_dev)
> >>>>  		if (ret)
> >>>>  			return ret;
> >>>>  	}
> >>>> -	dma_set_max_seg_size(dev, UINT_MAX);
> >>>> +	dma_set_max_seg_size(dev, SZ_2G);
> >>>
> >>> Are you sure? What do you think this does in the RDMA stack?
> >>>
> >>
> >> This is the maximum DMA segment size when mapping ULP's scatter/gather
> >> list to DMA address, right?
> > 
> > Yes, but only for ib_sge
> > 
> > But I think there are other possible problems if your HW cannot
> > implement the full ib_sge :\
> 
> Why? According to IB spec, the maximum RDMA messgae size is 2GB,
> so IMHO supporting ib_sge with DMA size larger than 2GB doesn't
> seem to have much practical meaning.

I'm not sure we comprehensively check that everywhere..

Jason