linux-kernel - Re: [PATCH bpf-next v3 1/3] xsk: Support UMEM chunk_size > PAGE

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Message-ID: <CAHApi-=ODe-WtJ=m6bycQhKoQxb+kk2Yk9Fx5SgBsWUuWT_u-A@mail.gmail.com>
Date:   Fri, 14 Apr 2023 18:36:04 +0200
From:   Kal Cutter Conley <kal.conley@...tris.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 1/3] xsk: Support UMEM chunk_size > PAGE_SIZE

> In addition, presumably when using this mode, the other XDP actions
> (XDP_PASS, XDP_REDIRECT to other targets) would stop working unless we
> add special handling for that in the kernel? We'll definitely need to
> handle that somehow...

I am not familiar with all the details here. Do you know a reason why
these cases would stop working / why special handling would be needed?
For example, if I have a UMEM that uses hugepages and XDP_PASS is
returned, then the data is just copied into an SKB right? SKBs can
also be created directly from hugepages AFAIK. So I don't understand
what the issue would be. Can someone explain this concern?