linux-kernel - Re: [PATCH v2 00/19] Add generic vdso

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Date:   Thu, 26 Nov 2020 20:41:02 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Guo Ren <guoren@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 00/19] Add generic vdso_base tracking

Hi Christophe,

On 11/24/20 6:53 AM, Christophe Leroy wrote:
> 
> 
> Le 24/11/2020 à 01:29, Dmitry Safonov a écrit :
>> v2 Changes:
>> - Rename user_landing to vdso_base as it tracks vDSO VMA start address,
>>    rather than the explicit address to land (Andy)
>> - Reword and don't use "new-execed" and "new-born" task (Andy)
>> - Fix failures reported by build robot
>>
>> Started from discussion [1], where was noted that currently a couple of
>> architectures support mremap() for vdso/sigpage, but not munmap().
>> If an application maps something on the ex-place of vdso/sigpage,
>> later after processing signal it will land there (good luck!)
>>
>> Patches set is based on linux-next (next-20201123) and it depends on
>> changes in x86/cleanups (those reclaim TIF_IA32/TIF_X32) and also
>> on my changes in akpm (fixing several mremap() issues).
> 
> I have a series that cleans up VDSO init on powerpc and migrates powerpc
> to _install_special_mapping() (patch 10 of the series).
> 
> https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=204396&state=%2A&archive=both
> 
> 
> I'm wondering how we should coordinate with your series for merging.
> 
> I guess your series will also imply removal of arch_unmap() ? see
> https://elixir.bootlin.com/linux/v5.10-rc4/source/arch/powerpc/include/asm/mmu_context.h#L262

I think our series intersect only in that moment where I re-introduce
arch_setup_additional_pages() parameters. So, in theory we could
minimize the conflicts by merging both series in parallel and cleanup
the result by moving to generic vdso_base on the top, what do you think?

Thanks,
          Dmitry