netdev - Re: [PATCH v3 net-next 0/7] net: ethernet: ti: cpsw: Add XDP support

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Date:   Thu, 6 Jun 2019 10:08:50 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     ivan.khoronzhuk@...aro.org, grygorii.strashko@...com,
        hawk@...nel.org, ast@...nel.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, xdp-newbies@...r.kernel.org,
        ilias.apalodimas@...aro.org, netdev@...r.kernel.org,
        daniel@...earbox.net, jakub.kicinski@...ronome.com,
        john.fastabend@...il.com, brouer@...hat.com
Subject: Re: [PATCH v3 net-next 0/7] net: ethernet: ti: cpsw: Add XDP
 support

On Wed, 05 Jun 2019 12:14:50 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
> Date: Wed,  5 Jun 2019 16:20:02 +0300
> 
> > This patchset adds XDP support for TI cpsw driver and base it on
> > page_pool allocator. It was verified on af_xdp socket drop,
> > af_xdp l2f, ebpf XDP_DROP, XDP_REDIRECT, XDP_PASS, XDP_TX.  
> 
> Jesper et al., please give this a good once over.

The issue with merging this, is that I recently discovered two bug with
page_pool API, when using DMA-mappings, which result in missing
DMA-unmap's.  These bugs are not "exposed" yet, but will get exposed
now with this drivers.  

The two bugs are:

#1: in-flight packet-pages can still be on remote drivers TX queue,
while XDP RX driver manage to unregister the page_pool (waiting 1 RCU
period is not enough).

#2: this patchset also introduce page_pool_unmap_page(), which is
called before an XDP frame travel into networks stack (as no callback
exist, yet).  But the CPUMAP redirect *also* needs to call this, else we
"leak"/miss DMA-unmap.

I do have a working prototype, that fixes these two bugs.  I guess, I'm
under pressure to send this to the list soon...

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer