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From:   Marco Elver <elver@google.com>
Date:   Mon, 18 Jul 2022 16:26:25 +0200
Message-ID: <CANpmjNPhhPUZFSZaLbwyJfACWMOqFchvm-Sx+iwGSM3sxkky8Q@mail.gmail.com>
Subject: Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early
 allocated pool
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>, yee.lee@mediatek.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "open list:KFENCE" <kasan-dev@googlegroups.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@lists.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>
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On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
[...]
> > - This patch has been accused of crashing the kernel:
> >
> >         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
> >
> >   Do we think that report is bogus?
>
> I think all of this is highly architecture-specific...

The report can be reproduced on i386 with CONFIG_X86_PAE=y. But e.g.
mm/memblock.c:memblock_free() is also guilty of using __pa() on
previously memblock_alloc()'d addresses. Looking at the phys addr
before memblock_alloc() does virt_to_phys(), the result of __pa()
looks correct even on PAE, at least for the purpose of passing it on
to kmemleak(). So I don't know what that BUG_ON(slow_virt_to_phys() !=
phys_addr) is supposed to tell us here.

Ideas?