linux-kernel - Re: [PATCH] mm: Add new vma flag VM_LOCAL

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Date:   Tue, 15 May 2018 13:47:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boaz Harrosh <boazh@...app.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Amit Golander <Amit.Golander@...app.com>
Subject: Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU

On Tue, May 15, 2018 at 01:43:23PM +0300, Boaz Harrosh wrote:
> Yes I know, but that is exactly the point of this flag. I know that this
> address is only ever accessed from a single core. Because it is an mmap (vma)
> of an O_TMPFILE-exclusive file created in a core-pinned thread and I allow
> only that thread any kind of access to this vma. Both the filehandle and the
> mmaped pointer are kept on the thread stack and have no access from outside.
> 
> So the all point of this flag is the kernel driver telling mm that this
> address is enforced to only be accessed from one core-pinned thread.

What happens when the userspace part -- there is one, right, how else do
you get an mm to stick a vma in -- simply does a full address range
probe scan?

Something like this really needs a far more detailed Changelog that
explains how its to be used and how it is impossible to abuse. Esp. that
latter is _very_ important.