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

From: Jesper Dangaard Brouer
Date: Thu Jun 06 2019 - 04:13:09 EST

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

> From: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
> 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