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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 7 Jan 2021 11:47:02 -0800
Message-ID: <CAHk-=wh+KfbJ4Wrz4A+hFRRj7ZYWysz9L8s-BosC3bhV6vN-nQ@mail.gmail.com>
Subject: Re: [BUG] from x86: Support kmap_local() forced debugging
To:     Willem de Bruijn <willemb@google.com>
Cc:     Jakub Kicinski <kuba@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        David Miller <davem@davemloft.net>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Netdev <netdev@vger.kernel.org>
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On Wed, Jan 6, 2021 at 8:45 PM Willem de Bruijn <willemb@google.com> wrote:
>
> But there are three other kmap_atomic callers under net/ that do not
> loop at all, so assume non-compound pages. In esp_output_head,
> esp6_output_head and skb_seq_read. The first two directly use
> skb_page_frag_refill, which can allocate compound (but not
> __GFP_HIGHMEM) pages, and the third can be inserted with
> netfilter xt_string in the path of tcp transmit skbs, which can also
> have compound pages. I think that these could similarly access
> data beyond the end of the kmap_atomic mapped page. I'll take
> a closer look.

Thanks.

Note that I have flushed my random one-liner patch from my system, and
expect to get a proper fix through the normal networking pulls.

And _if_ the networking people feel that my one-liner was the proper
fix, you can use it and add my sign-off if you want to, but it really
was more of a "this is the quick ugly fix for testing" rather than
anything else.

          Linus