Date: Thu, 17 Mar 2016 17:42:26 +0000
From: Olu Ogunbowale <olu.ogunbowale@imgtec.com>
To: Jerome Glisse <j.glisse@gmail.com>
CC: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Michel Lespinasse <walken@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>,
        Russell King <linux@arm.linux.org.uk>,
        Ralf Baechle <ralf@linux-mips.org>, Paul Mundt <lethal@linux-sh.org>,
        "David S. Miller" <davem@davemloft.net>,
        Chris Metcalf <cmetcalf@tilera.com>, Ingo Molnar <mingo@elte.hu>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Jackson DSouza <Jackson.DSouza@imgtec.com>
Subject: Re: [PATCH] mm: Export symbols unmapped_area() &
 unmapped_area_topdown()
Message-ID: <20160317174226.GC31608@imgtec.com>
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 <20160317143714.GA16297@gmail.com>
 <20160317154635.GA31608@imgtec.com>
 <20160317170348.GB16297@gmail.com>
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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.