Re: [PATCH for-next v2 06/18] RDMA/rxe: Add rxe_add_frag() to rxe_mr.c

Bob Pearson
2022-12-01T17:11:15Z

On 12/1/22 09:39, Jason Gunthorpe wrote:
> On Thu, Dec 01, 2022 at 09:38:10AM -0600, Bob Pearson wrote:
>
>> Further, looking at ipoib as an example, it builds sge lists using the lkey from get_dma_mr()
>> and sets the sge->addr to a kernel virtual memory address after previously calling
>> ib_dma_map_single() so the addresses are mapped for dma access and visible before use.
>> They are unmapped after the read/write operation completes. What is the point of kmapping
>> the address after dma mapping them?
>
> Because not everything is ipoib, and things like block will map sgls
> with struct pages, not kva.
>
> Jason

OK it's working now but there is a bug in your rxe_mr_fill_pages_from_sgt() routine.
You have a

if (xas_xa_index && WARN_ON(sg_iter.sg_pgoffset % PAGE_SIZE)) {...}

which seems to assume that sg_pgoffset contains the byte offset in the current page.
But looking at __sg_page_iter_next() it appears that it is the number of pages offset
in the current sg entry which results in a splat when I run ib_send_bw.

Bob