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From: Daniel Axtens <dja@axtens.net>
To: Michael Ellerman <mpe@ellerman.id.au>, Michal =?utf-8?Q?Such=C3=A1nek?=
 <msuchanek@suse.de>
Subject: Re: [PATCH] powerpc/fault: kernel can extend a user process's stack
In-Reply-To: <878sfethsj.fsf@mpe.ellerman.id.au>
References: <20191211014337.28128-1-dja@axtens.net>
 <20191211072806.GI3986@kitsune.suse.cz>
 <8736drciem.fsf@dja-thinkpad.axtens.net>
 <20200720105116.GO32107@kitsune.suse.cz> <878sfethsj.fsf@mpe.ellerman.id.au>
Date: Tue, 21 Jul 2020 10:57:52 +1000
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Cc: Tom Lane <tgl@sss.pgh.pa.us>, linuxppc-dev@lists.ozlabs.org,
 Daniel Black <daniel@linux.ibm.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Michael Ellerman <mpe@ellerman.id.au> writes:

> Michal Such=C3=A1nek <msuchanek@suse.de> writes:
>> Hello,
>>
>> On Wed, Dec 11, 2019 at 08:37:21PM +1100, Daniel Axtens wrote:
>>> > Fixes: 14cf11af6cf6 ("powerpc: Merge enough to start building in
>>> > arch/powerpc.")
>>>=20
>>> Wow, that's pretty ancient! I'm also not sure it's right - in that same
>>> patch, arch/ppc64/mm/fault.c contains:
>>>=20
>>> ^1da177e4c3f4 (Linus Torvalds         2005-04-16 15:20:36 -0700 213)   =
         if (address + 2048 < uregs->gpr[1]
>>> ^1da177e4c3f4 (Linus Torvalds         2005-04-16 15:20:36 -0700 214)   =
             && (!user_mode(regs) || !store_updates_sp(regs)))
>>> ^1da177e4c3f4 (Linus Torvalds         2005-04-16 15:20:36 -0700 215)   =
                 goto bad_area;
>>>=20
>>> Which is the same as the new arch/powerpc/mm/fault.c code:
>>>=20
>>> 14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 234)           =
 if (address + 2048 < uregs->gpr[1]
>>> 14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 235)           =
     && (!user_mode(regs) || !store_updates_sp(regs)))
>>> 14cf11af6cf60 (Paul Mackerras 2005-09-26 16:04:21 +1000 236)           =
         goto bad_area;
>>>=20
>>> So either they're both right or they're both wrong, either way I'm not
>>> sure how this patch is to blame.
>>
>> Is there any progress on resolving this?
>>
>> I did not notice any followup patch nor this one being merged/refuted.
>
> It ended up with this:
>
> https://lore.kernel.org/linuxppc-dev/20200703141327.1732550-2-mpe@ellerma=
n.id.au/
>
>
> Which I was hoping would get some reviews :)

Ah, I missed this. I'll give it a look as soon as I can.

Kind regards,
Daniel

>
> I'll probably merge the whole series into next this week.
>
> cheers