linux-kernel - Re: [PATCH v4 bpf 0/4] vmalloc: bpf: introduce VM_ALLOW_HUGE

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Message-ID: <CAHk-=wiQcg=7++Odg08=eZZgdX4NKcPqiqGKXHNXqesTtfkmmA@mail.gmail.com>
Date:   Thu, 21 Apr 2022 09:15:05 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc:     "npiggin@...il.com" <npiggin@...il.com>,
        "songliubraving@...com" <songliubraving@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "Kernel-team@...com" <Kernel-team@...com>,
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Subject: Re: [PATCH v4 bpf 0/4] vmalloc: bpf: introduce VM_ALLOW_HUGE_VMAP

On Thu, Apr 21, 2022 at 8:47 AM Edgecombe, Rick P
<rick.p.edgecombe@...el.com> wrote:
>
>                 I wonder if it
> might have to do with the vmalloc huge pages using compound pages, then
> some caller doing vmalloc_to_page() and getting surprised with what
> they could get away with in the struct page.

Very likely. We have 100+ users of vmalloc_to_page() in random
drivers, and the gpu code does show up on that list.

And is very much another case of "it's always been broken, but
enabling it on x86 made the breakage actually show up in real life".

                   Linus