linux-kernel - Re: [PATCH 0/2] Tracking user space vDSO remaping

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Date:	Wed, 2 Mar 2016 07:13:10 -0500
From:	Christopher Covington <cov@...eaurora.org>
To:	Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Guan Xuetao <gxt@...c.pku.edu.cn>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net,
	user-mode-linux-user@...ts.sourceforge.net,
	linux-arch@...r.kernel.org, linux-mm@...ck.org, criu@...nvz.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <Will.Deacon@....com>,
	Laura Abbott <labbott@...oraproject.org>,
	David Brown <david.brown@...aro.org>
Subject: Re: [PATCH 0/2] Tracking user space vDSO remaping

Hi,

On 03/20/2015 11:53 AM, Laurent Dufour wrote:
> CRIU is recreating the process memory layout by remapping the checkpointee
> memory area on top of the current process (criu). This includes remapping
> the vDSO to the place it has at checkpoint time.
> 
> However some architectures like powerpc are keeping a reference to the vDSO
> base address to build the signal return stack frame by calling the vDSO
> sigreturn service. So once the vDSO has been moved, this reference is no
> more valid and the signal frame built later are not usable.
> 
> This patch serie is introducing a new mm hook 'arch_remap' which is called
> when mremap is done and the mm lock still hold. The next patch is adding the
> vDSO remap and unmap tracking to the powerpc architecture.
> 
> Laurent Dufour (2):
>   mm: Introducing arch_remap hook
>   powerpc/mm: Tracking vDSO remap
> 
>  arch/powerpc/include/asm/mmu_context.h   | 35 +++++++++++++++++++++++++++++++-
>  arch/s390/include/asm/mmu_context.h      |  6 ++++++
>  arch/um/include/asm/mmu_context.h        |  5 +++++
>  arch/unicore32/include/asm/mmu_context.h |  6 ++++++
>  arch/x86/include/asm/mmu_context.h       |  6 ++++++
>  include/asm-generic/mm_hooks.h           |  6 ++++++
>  mm/mremap.c                              |  9 ++++++--
>  7 files changed, 70 insertions(+), 3 deletions(-)

We would like to be able to remap/unmap the VDSO on arm and arm64 as
well. When I proposed a patch with mmu_context.h and mmu-arch-hooks.h
changes to arm64 that were nearly identical to those done to powerpc,
Will Deacon reasonably suggested [1] attempting to combine the code and
provide generic VDSO accessors. Unfortunately, I no prior experience
with generic MM code. Can anyone advise on how to get started with that?

1. http://www.spinics.net/lists/linux-arm-msm/msg18441.html

Thanks,
Christopher Covington

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