From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Sat, 21 Jul 2012 15:35:17 +0100
Subject: [PATCH] ARM: mm: avoid attempting to flush the gate_vma with
 VIVT caches
In-Reply-To: <500AAC2B.5060300@xenomai.org>
References: <1342455826-9425-1-git-send-email-will.deacon@arm.com>
 <20120719122814.GE29153@mudshark.cambridge.arm.com>
 <5009C26B.6080901@xenomai.org> <500AAC2B.5060300@xenomai.org>
Message-ID: <20120721143517.GB26790@mudshark.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Gilles,

On Sat, Jul 21, 2012 at 02:18:35PM +0100, Gilles Chanteperdrix wrote:
> On 07/20/2012 10:41 PM, Gilles Chanteperdrix wrote:
> > Being 0 or 1 whether we want to flush the vector page (I believe we do
> > not want to flush it, but am not sure).
> 
> Actually, I believe we want to flush the vector page, at least on
> systems with VIVT cache: on systems with VIVT cache, the vector page is
> writeable in kernel mode, so may have been modified, and the address
> used by elf_core_dump is not the vectors address, but the address in the
> kernel direct-mapped RAM region where the vector page was allocated, so
> there is a cache aliasing issue.

It may be writable, but we never actually write to it after it has been
initialised so there's no need to worry about caching issues (the cache is
flushed in devicemaps_init).

As for the NULL check, it's likely to be a single additional cycle
before a cacheflush. I really consider it to be insignificant.

Will