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From: Sagi Grimberg <sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org>
Subject: Re: RDMA Read: Local protection error
Date: Sun, 29 May 2016 11:37:13 +0300
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Cc: Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>, Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>, Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>, Yishai Hadas <yishaih-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>, Yishai Hadas <yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, linux-rdma <linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, Joonsoo Kim <iamjoonsoo.kim-Hm3cg6mZ9cc@public.gmane.org>, Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>, Majd Dibbiny <majd-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
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>> But this is specific to mlx4 which supports up 511 pages per MR, mlx5
>> will need a coherent allocation anyways right (it supports up to 64K
>> pages per MR)?
>
> Why does that make a difference?

Chuck's original bug report said that the problem with the current
code is that dma_map_single expects the pages array to fit in a single
page:

"
See what mlx4_alloc_priv_pages does with this memory
allocation:

   mr->page_map = dma_map_single(device->dma_device, mr->pages,
                                 size, DMA_TO_DEVICE);

dma_map_single() expects the mr->pages allocation to fit
on a single page, as far as I can tell.
"

But when I revisited dma_map_single in some archs I didn't
see this expectation. So actually now I don't really see what
is the problem in the first place (or how your patch fixes it)...
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