linux-kernel - Re: [RFC PATCH 01/17] perf: Allow mmapping only user page

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Message-ID: <20170906162847.7njgdzeioah2wdgm@pd.tnic>
Date:   Wed, 6 Sep 2017 18:28:47 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        acme@...hat.com, kirill.shutemov@...ux.intel.com, rric@...nel.org
Subject: Re: [RFC PATCH 01/17] perf: Allow mmapping only user page

On Tue, Sep 05, 2017 at 04:30:10PM +0300, Alexander Shishkin wrote:
> The 'user page' contains offsets and sizes of data and aux areas of the
> ring buffer. If a user wants to mmap a pre-existing buffer, they need to
> know these in order to issue mmap()s with correct offsets and sizes.

Ok, stupid question: shouldn't this be a properly defined interface
instead of allowing userspace to poke inside the user page? Or are we
prepared to handle any changes in the layout of that user page and there
won't be any userspace crying because of it?

Thx.

-- 
Regards/Gruss,
    Boris.

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