linux-kernel - Re: [PATCH] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP

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Message-ID: <alpine.DEB.2.20.1711131642370.1851@nanos>
Date:   Mon, 13 Nov 2017 16:43:26 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
cc:     Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Nicholas Piggin <npiggin@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Do not allow non-MAP_FIXED mapping across
 DEFAULT_MAP_WINDOW border

On Tue, 7 Nov 2017, Kirill A. Shutemov wrote:

> In case of 5-level paging, we don't put any mapping above 47-bit, unless
> userspace explicitly asked for it.
> 
> Userspace can ask for allocation from full address space by specifying
> hint address above 47-bit.
> 
> Nicholas noticed that current implementation violates this interface:
> we can get vma partly in high addresses if we ask for a mapping at very
> end of 47-bit address space.
> 
> Let's make sure that, when consider hint address for non-MAP_FIXED
> mapping, start and end of resulting vma are on the same side of 47-bit
> border.

What happens for mappings with MAP_FIXED which cross the border?

Thanks,

	tglx