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powerpc/vdso: Separate vvar vma from vdso
commit 1c4bce6 upstream. Since commit 511157a ("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 511157a 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! [1]: checkpoint-restore/criu#1417 Cc: stable@vger.kernel.org # v5.11 Signed-off-by: Dmitry Safonov <dima@arista.com> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> # vDSO parts. Acked-by: Andrei Vagin <avagin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/f401eb1ebc0bfc4d8f0e10dc8e525fd409eb68e2.1617209142.git.christophe.leroy@csgroup.eu Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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