linux-kernel - Re: [PATCH v3 00/23] Add generic vdso

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Message-ID: <6b2513db-7c31-8da4-38ec-0b9898c6589c@arista.com>
Date:   Thu, 10 Mar 2022 21:17:58 +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
Subject: Re: [PATCH v3 00/23] Add generic vdso_base tracking

Hi Christophe,

On 3/9/22 15:41, Christophe Leroy wrote:
> Hi Dmitry,
> 
> I'm wondering the status of this series.

Yeah, I plan to work on v4 addressing the reviews.
WFH has quite affected my work on side-projects and I've laid aside for
a while this patch set that touches every architecture and is besides
a bit challenging to upstream.

> Wondering what to do while reviewing pending powerpc patches and
> especially
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20201103171336.98883-1-ldufour@linux.ibm.com/

Please, go ahead with that - I'll base v4 patches on the top of that.
Thanks for pinging me about this.

> Christophe
> 
> Le 11/06/2021 à 20:02, Dmitry Safonov a écrit :
>> v3 Changes:
>> - Migrated arch/powerpc to vdso_base
>> - Added x86/selftest for unmapped vdso & no landing on fast syscall
>> - Review comments from Andy & Christophe (thanks!)
>> - Amended s/born process/execed process/ everywhere I noticed
>> - Build robot warning on cast from __user pointer
>>
>> I've tested it on x86, I would appreciate any help with
>> Tested-by on arm/arm64/mips/powerpc/s390/... platforms.
>>
>> One thing I've noticed while cooking this and haven't found a clean
>> way to solve is zero-terminated .pages[] array in vdso mappings, which
>> is not always zero-terminated but works by the reason of
>> VM_DONTEXPAND on mappings.
>>
>> 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).
>>
>> Logically, the patches set divides on:
>> - patch       1: a cleanup for patches in x86/cleanups
>> - patches  2-13: cleanups for arch_setup_additional_pages()
>> - patches 13-14: x86 signal changes for unmapped vdso
>> - patches 15-22: provide generic vdso_base in mm_struct
>> - patch      23: selftest for unmapped vDSO & fast syscalls
>>
>> In the end, besides cleanups, it's now more predictable what happens for
>> applications with unmapped vdso on architectures those support .mremap()
>> for vdso/sigpage.
>>
>> I'm aware of only one user that unmaps vdso - Valgrind [2].
>> (there possibly are more, but this one is "special", it unmaps vdso, but
>>   not vvar, which confuses CRIU [Checkpoint Restore In Userspace], that's
>>   why I'm aware of it)
>>
> 
> I'm wondering the status of this series.
> 
> Wondering what to do while reviewing pending powerpc patches and
> especially
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20201103171336.98883-1-ldufour@linux.ibm.com/
> 
> 
> Christophe
> 


Thanks,
          Dmitry