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

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Message-ID: <20160903000800.GY2356@ZenIV.linux.org.uk>
Date:   Sat, 3 Sep 2016 01:08:01 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Dmitry Safonov <dsafonov@...tuozzo.com>,
        "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>
Subject: Re: [RFC 1/3] x86/vdso: create vdso file, use it for mapping

On Mon, Aug 29, 2016 at 02:28:08AM -0700, 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.
> 
> Also, could this be simplified to use anon_inode?

Please, don't.  anon_inode is for situations when you don't mind sharing
the _same_ inode for different things.  This one very clearly isn't that.