linux-kernel - Re: [PATCH] mm: Export symbols unmapped_area() & unmapped_area

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Message-ID: <20160317174226.GC31608@imgtec.com>
Date:	Thu, 17 Mar 2016 17:42:26 +0000
From:	Olu Ogunbowale <olu.ogunbowale@...tec.com>
To:	Jerome Glisse <j.glisse@...il.com>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Russell King <linux@....linux.org.uk>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jackson DSouza <Jackson.DSouza@...tec.com>
Subject: Re: [PATCH] mm: Export symbols unmapped_area() &
 unmapped_area_topdown()

On Thu, Mar 17, 2016 at 06:03:50PM +0100, Jerome Glisse wrote:
> Well trick still works, if driver is loaded early during userspace program
> initialization then you force mmap to specific range inside the driver
> userspace code. If driver is loaded after and program is already using those
> range then you can register a notifier to track when those range. If they
> get release by the program you can have the userspace driver force creation
> of new reserve vma again.

I should have been more clearer in my response, this applies only because
we are in a scheme were all allocations must go through a special allocator 
because VMA base/range is reserved for SVM.

> Well controling range into which VMA can be allocated is not something that
> you should do lightly (thing like address space randomization would be
> impacted). And no the SVM range is not upper bound by the amount of memory
> but by the physical bus size if it is 48bits nothing forbid to put all the
> program memory above 8GB and nothing below. We are talking virtual address
> here. By the way i think most 64 bit ARM are 40 bits and it seems a shame
> for GPU to not go as high as the CPU.

Same as above. By the way, we support minimum 40-bits but can be paired with
CPU(s) of higher bits; no problem if bits are equal or greater than CPU.