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

From: Jesper Dangaard Brouer <[email-masked]>
Date: Thu, 6 Jun 2019 10:08:50 +0200

On Wed, 05 Jun 2019 12:14:50 -0700 (PDT)
David Miller <[email-masked]> wrote:

> From: Ivan Khoronzhuk <[email-masked]>
> 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