linux-kernel - Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings

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Message-ID: <20191030071136.GA20624@rapoport-lnx>
Date:   Wed, 30 Oct 2019 08:11:37 +0100
From:   Mike Rapoport <rppt@...nel.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        linux-kernel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-api@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user
 mappings

On Tue, Oct 29, 2019 at 10:12:04AM +0000, Christopher Lameter wrote:
> 
> 
> On Tue, 29 Oct 2019, Mike Rapoport wrote:
> 
> > I've talked with Thomas yesterday and he suggested something similar:
> >
> > When the MAP_EXCLUSIVE request comes for the first time, we allocate a huge
> > page for it and then use this page as a pool of 4K pages for subsequent
> > requests. Once this huge page is full we allocate a new one and append it
> > to the pool. When all the 4K pages that comprise the huge page are freed
> > the huge page is collapsed.
> 
> Or write a device driver that allows you to mmap a secure area and avoid
> all core kernel modifications?
> 
> /dev/securemem or so?

A device driver will need to remove the secure area from the direct map and
then we back to square one.
 
> It may exist already.
> 

-- 
Sincerely yours,
Mike.