linux-kernel - Re: [RFC 1/3] x86/vdso: create vdso file, use it for mapping

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Date:   Tue, 30 Aug 2016 07:58:07 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Dmitry Safonov <dsafonov@...tuozzo.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC 1/3] x86/vdso: create vdso file, use it for mapping

On Mon, Aug 29, 2016 at 2:50 AM, Dmitry Safonov <dsafonov@...tuozzo.com> wrote:
> On 08/29/2016 12:28 PM, Andy Lutomirski wrote:
>>
>> On Thu, Aug 25, 2016 at 8:21 AM, Dmitry Safonov <dsafonov@...tuozzo.com>
>> wrote:
>>>
>>> I added here a new in-kernel fs with ramfs-like options.
>>> Created vdso file in this fs (yet for testing, only 64-bit vdso).
>>> Mapped this file to process's mm on setup_additional_pages.
>>> Just for testing purpose it's done only for specific UID.
>>
>>
>> I'm wondering whether all this code could be easily moved into the
>> core special mapping helpers so that all special mappings get the same
>> benefit.  We could embed a struct file * (or struct inode or whatever)
>> in special_mapping if needed.
>
>
> Hmm, yes, I guess. The only thing -- we'll still need per-arch changes
> to initialize those files on booting. But that looks like the proper
> generic place to move this code.

You might be able to get away with initializing on first use.

--Andy