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

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Message-ID: <8bba9ed8-ae1f-7c98-fde5-808927935447@csgroup.eu>
Date:   Wed, 9 Mar 2022 16:41:29 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Dmitry Safonov <dima@...sta.com>, 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 Dmitry,

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

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