linux-kernel - Re: [PATCHv2 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO

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Date:	Tue, 2 Aug 2016 13:59:40 +0300
From:	Dmitry Safonov <dsafonov@...tuozzo.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	Michal Hocko <mhocko@...e.com>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Safonov <0x7f454c46@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Ingo Molnar" <mingo@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>, <xemul@...tuozzo.com>,
	Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCHv2 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_*

On 07/12/2016 05:14 PM, Oleg Nesterov wrote:
> On 07/11, Andy Lutomirski wrote:
>> I'm starting to wonder if we should finally suck it up and give
>> special mappings a non-NULL vm_file so we can track them properly.
>> Oleg, weren't you thinking of doing that for some other reason?
>
> Yes, uprobes. Currently we can't probe vdso page(s).

So, to make sure, that I've understood correctly, I need to:
o add vm_file to vdso/vvar vmas, __install_special_mapping will init
   them;
o place array pages[] inside f_mapping;
o create f_inode for each file -- for this we need some mount point, so
   I'll create something like vdsofs, register this filesystem and mount
   it in initcall (or like do_basic_setup - as it's done by shmem, i.e).

Is this the idea, or I got it wrong?

And maybe the idea is to create fake vm_file for just reference
counting, but do not treat/init it like file with inode, etc?
So with fake file I can also check if vdso is mapped already, but
I'm sure the fake file will not help Oleg with uprobes.

-- 
              Dmitry