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Date:   Fri, 24 Apr 2020 16:04:04 +0200
From:   Toke Høiland-Jørgensen <>
To:     Jesper Dangaard Brouer <>,
Cc:     Jesper Dangaard Brouer <>,,,,,, Daniel Borkmann <>,
        Alexei Starovoitov <>,
        John Fastabend <>,
        Alexander Duyck <>,
        Jeff Kirsher <>,
        David Ahern <>,
        Willem de Bruijn <>,
        Ilias Apalodimas <>,
        Lorenzo Bianconi <>,
        Saeed Mahameed <>,
Subject: Re: [PATCH net-next 07/33] xdp: xdp_frame add member frame_sz and handle in convert_to_xdp_frame

Jesper Dangaard Brouer <> writes:

> Use hole in struct xdp_frame, when adding member frame_sz, which keeps
> same sizeof struct (32 bytes)
> Drivers ixgbe and sfc had bug cases where the necessary/expected
> tailroom was not reserved. This can lead to some hard to catch memory
> corruption issues. Having the drivers frame_sz this can be detected when
> packet length/end via xdp->data_end exceed the xdp_data_hard_end
> pointer, which accounts for the reserved the tailroom.
> When detecting this driver issue, simply fail the conversion with NULL,
> which results in feedback to driver (failing xdp_do_redirect()) causing
> driver to drop packet. Given the lack of consistent XDP stats, this can
> be hard to troubleshoot. And given this is a driver bug, we want to
> generate some more noise in form of a WARN stack dump (to ID the driver
> code that inlined convert_to_xdp_frame).
> Inlining the WARN macro is problematic, because it adds an asm
> instruction (on Intel CPUs ud2) what influence instruction cache
> prefetching. Thus, introduce xdp_warn and macro XDP_WARN, to avoid this
> and at the same time make identifying the function and line of this
> inlined function easier.
> Signed-off-by: Jesper Dangaard Brouer <>

Acked-by: Toke Høiland-Jørgensen <>

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