Re: [PATCH] powerpc/vdso: Separate vvar vma from vdso

From: Dmitry Safonov <dima@arista.com>
To: Laurent Dufour <ldufour@linux.ibm.com>, linux-kernel@vger.kernel.org
Cc: Dmitry Safonov <0x7f454c46@gmail.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Andrei Vagin <avagin@gmail.com>,
	Andy Lutomirski <luto@kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Paul Mackerras <paulus@samba.org>,
	linuxppc-dev@lists.ozlabs.org, stable@vger.kernel.org
Subject: Re: [PATCH] powerpc/vdso: Separate vvar vma from vdso
Date: Mon, 29 Mar 2021 20:59:35 +0100	[thread overview]
Message-ID: <50b7a78a-76e6-7d28-5324-a3ada9c43019@arista.com> (raw)
In-Reply-To: <f97f3ff9-6ae2-64cc-fada-49fcac34ae47@linux.ibm.com>

On 3/29/21 4:14 PM, Laurent Dufour wrote:
> Le 26/03/2021 à 20:17, Dmitry Safonov a écrit :
>> Since commit 511157ab641e ("powerpc/vdso: Move vdso datapage up front")
>> VVAR page is in front of the VDSO area. In result it breaks CRIU
>> (Checkpoint Restore In Userspace) [1], where CRIU expects that "[vdso]"
>> from /proc/../maps points at ELF/vdso image, rather than at VVAR data
>> page.
>> Laurent made a patch to keep CRIU working (by reading aux vector).
>> But I think it still makes sence to separate two mappings into different
>> VMAs. It will also make ppc64 less "special" for userspace and as
>> a side-bonus will make VVAR page un-writable by debugger (which
>> previously
>> would COW page and can be unexpected).
>>
>> I opportunistically Cc stable on it: I understand that usually such
>> stuff isn't a stable material, but that will allow us in CRIU have
>> one workaround less that is needed just for one release (v5.11) on
>> one platform (ppc64), which we otherwise have to maintain.
>> I wouldn't go as far as to say that the commit 511157ab641e is ABI
>> regression as no other userspace got broken, but I'd really appreciate
>> if it gets backported to v5.11 after v5.12 is released, so as not
>> to complicate already non-simple CRIU-vdso code. Thanks!
>>
>> Cc: Andrei Vagin <avagin@gmail.com>
>> Cc: Andy Lutomirski <luto@kernel.org>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
>> Cc: Laurent Dufour <ldufour@linux.ibm.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: linuxppc-dev@lists.ozlabs.org
>> Cc: stable@vger.kernel.org # v5.11
>> [1]: https://github.com/checkpoint-restore/criu/issues/1417
>> Signed-off-by: Dmitry Safonov <dima@arista.com>
>> Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> 
> I run the CRIU's test suite and except the usual suspects, all the tests
> passed.
> 
> Tested-by: Laurent Dufour <ldufour@linux.ibm.com>

Thank you, Laurent!

-- 
          Dmitry