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

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Message-ID: <alpine.DEB.2.21.1910290706360.3769@www.lameter.com>
Date:   Tue, 29 Oct 2019 07:08:42 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
cc:     Mike Rapoport <rppt@...nel.org>, 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 Mon, 28 Oct 2019, Kirill A. Shutemov wrote:

> Setting a single 4k page non-present in the direct mapping will require
> splitting 2M or 1G page we usually map direct mapping with. And it's one
> way road. We don't have any mechanism to map the memory with huge page
> again after the application has freed the page.
>
> It might be okay if all these pages cluster together, but I don't think we
> have a way to achieve it easily.

Set aside a special physical memory range for this and migrate the
page to that physical memory range when MAP_EXCLUSIVE is specified?

Maybe some processors also have hardware ranges that offer additional
protection for stuff like that?