linux-kernel - Re: [PATCH 01/22] ARM: add mechanism for late code patching

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Message-ID: <alpine.LFD.2.02.1208061356480.5231@xanadu.home>
Date:	Mon, 6 Aug 2012 14:02:19 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Cyril Chemparathy <cyril@...com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, catalin.marinas@....com, will.deacon@....com
Subject: Re: [PATCH 01/22] ARM: add mechanism for late code patching

On Mon, 6 Aug 2012, Russell King - ARM Linux wrote:

> On Mon, Aug 06, 2012 at 09:19:10AM -0400, Cyril Chemparathy wrote:
> > With a flush_cache_all(), we could avoid having to operate a cacheline  
> > at a time, but that clobbers way more than necessary.
> 
> You can't do that, because flush_cache_all() on some CPUs requires the
> proper MMU mappings to be in place, and you can't get those mappings
> in place because you don't have the V:P offsets fixed up in the kernel.
> Welcome to the chicken and egg problem.

This problem is fixed in this case by having the p2v and v2p code sites 
using an out-of-line non optimized computation until those sites are 
runtime patched with the inlined optimized computation we have today.


Nicolas
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