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Date:   Tue, 29 Oct 2019 07:08:42 +0000 (UTC)
From:   Christopher Lameter <cl@linux.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
cc:     Mike Rapoport <rppt@kernel.org>, linux-kernel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        James Bottomley <jejb@linux.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-api@vger.kernel.org,
        linux-mm@kvack.org, x86@kernel.org,
        Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user
 mappings
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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?