linux-kernel - RE: [PATCH v2 08/25] powerpc/8xx: Map IMMR area with 512k page at a fixed address

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CBA2CBE@AcuExch.aculab.com>
Date:	Fri, 25 Sep 2015 14:46:40 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Scott Wood' <scottwood@...escale.com>
CC:	'Christophe Leroy' <christophe.leroy@....fr>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	"Michael Ellerman" <mpe@...erman.id.au>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 08/25] powerpc/8xx: Map IMMR area with 512k page at a
 fixed address

From: Scott Wood
> Sent: 24 September 2015 21:14
> > Isn't this a more general problem?
> >
> > If there are multiple remap requests for the same physical page
> > shouldn't the kernel be just increasing a reference count somewhere
> > and returning address in the same virtual page?
> > This should probably happen regardless of the address.
> > I presume it must be done for cacheable mappings.
> 
> Why would you assume that?

Because 'really horrid (tm)' things happen on some cache
architectures if you map the same physical address to
multiple virtual addresses.

	David