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Date:   Sun, 4 Apr 2021 22:03:37 -0700
From:   Andrei Vagin <avagin@gmail.com>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        dima@arista.com, arnd@arndb.de, tglx@linutronix.de,
        vincenzo.frascino@arm.com, luto@kernel.org,
        linux-arch@vger.kernel.org
Subject: Re: [PATCH RESEND v1 3/4] powerpc/vdso: Separate vvar vma from vdso
Message-ID: <YGqaKYnLnvj2brJ8@gmail.com>
References: <cover.1617209141.git.christophe.leroy@csgroup.eu>
 <f401eb1ebc0bfc4d8f0e10dc8e525fd409eb68e2.1617209142.git.christophe.leroy@csgroup.eu>
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On Wed, Mar 31, 2021 at 04:48:46PM +0000, Christophe Leroy wrote:
> From: Dmitry Safonov <dima@arista.com>
> 
> 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>

Acked-by: 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>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>