linux-kernel - Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore

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Message-ID: <CANpmjNPhhPUZFSZaLbwyJfACWMOqFchvm-Sx+iwGSM3sxkky8Q@mail.gmail.com>
Date:   Mon, 18 Jul 2022 16:26:25 +0200
From:   Marco Elver <elver@...gle.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, yee.lee@...iatek.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:KFENCE" <kasan-dev@...glegroups.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early
 allocated pool

On Sat, 16 Jul 2022 at 20:43, Geert Uytterhoeven <geert@...ux-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?