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

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Message-ID: <20160317164034.GB31608@imgtec.com>
Date:	Thu, 17 Mar 2016 16:40:34 +0000
From:	Olu Ogunbowale <olu.ogunbowale@...tec.com>
To:	Rik van Riel <riel@...hat.com>
CC:	<inux-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>,
	Jerome Glisse <j.glisse@...il.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 Wed, Mar 16, 2016 at 05:00:41PM -0400, Rik van Riel wrote:
> 
> The drivers appear to require the HMM framework though,
> which people are also reluctant to merge without the
> drivers.
> 
> How do we get past this chicken & egg situation?

I would like to point out that support for HSA varies from
one vendor/design to another; for some device/drivers
(i.e AMD APU/HSA kernel driver), no form of address 
space mirroring is required (i.e. AMD IOMMU v2) AFAIK, 
others require address space mirroring so need the kernel
HMM framework but only because they provide support for 
the full HSA/OpenCL SVM specification while some do not 
require HMM at all because they implement only a subset
of the specification.

These exports enables the latter approach which does
not require the kernel HMM framework in order to 
support process address space mirroring.

Regards,
Olu