netdev - Re: [PATCH net-next 23/33] ixgbe: add XDP frame size to driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <69e05693-c3df-8f48-7a08-03bf4d58cb07@iogearbox.net>
Date:   Mon, 27 Apr 2020 21:51:50 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, sameehj@...zon.com
Cc:     intel-wired-lan@...ts.osuosl.org,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org, zorik@...zon.com,
        akiyano@...zon.com, gtzalik@...zon.com,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        David Ahern <dsahern@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        steffen.klassert@...unet.com
Subject: Re: [PATCH net-next 23/33] ixgbe: add XDP frame size to driver

On 4/22/20 6:09 PM, Jesper Dangaard Brouer wrote:
> This driver uses different memory models depending on PAGE_SIZE at
> compile time. For PAGE_SIZE 4K it uses page splitting, meaning for
> normal MTU frame size is 2048 bytes (and headroom 192 bytes). For
> larger MTUs the driver still use page splitting, by allocating
> order-1 pages (8192 bytes) for RX frames. For PAGE_SIZE larger than
> 4K, driver instead advance its rx_buffer->page_offset with the frame
> size "truesize".
> 
> For XDP frame size calculations, this mean that in PAGE_SIZE larger
> than 4K mode the frame_sz change on a per packet basis. For the page
> split 4K PAGE_SIZE mode, xdp.frame_sz is more constant and can be
> updated once outside the main NAPI loop.
> 
> The default setting in the driver uses build_skb(), which provides
> the necessary headroom and tailroom for XDP-redirect in RX-frame
> (in both modes).
> 
> There is one complication, which is legacy-rx mode (configurable via
> ethtool priv-flags). There are zero headroom in this mode, which is a
> requirement for XDP-redirect to work. The conversion to xdp_frame
> (convert_to_xdp_frame) will detect this insufficient space, and
> xdp_do_redirect() call will fail. This is deemed acceptable, as it
> allows other XDP actions to still work in legacy-mode. In
> legacy-mode + larger PAGE_SIZE due to lacking tailroom, we also
> accept that xdp_adjust_tail shrink doesn't work.
> 
> Cc: intel-wired-lan@...ts.osuosl.org
> Cc: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> Cc: Alexander Duyck <alexander.duyck@...il.com>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>

Alexander/Jeff, in case the ixgbe/i40e/ice changes look good to you,
please ack.

Thanks,
Daniel