linux-kernel - Re: [PATCH] flush icache before set_pte take6. [4/4] optimization for cpus other than montecito

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Message-ID: <46B05209.4050103@bull.net>
Date:	Wed, 01 Aug 2007 11:27:37 +0200
From:	Zoltan Menyhart <Zoltan.Menyhart@...l.net>
To:	Jim Hull <jim.hull@...com>
Cc:	'KAMEZAWA Hiroyuki' <kamezawa.hiroyu@...fujitsu.com>,
	'David Mosberger-Tang' <dmosberger@...il.com>,
	'LKML' <linux-kernel@...r.kernel.org>,
	linux-ia64@...r.kernel.org, tony.luck@...el.com,
	'Christoph Lameter' <clameter@....com>
Subject: Re: [PATCH] flush icache before set_pte take6. [4/4] optimization
 for cpus other than montecito

Jim Hull wrote:
> Not just crazy, but wrong - this *can* happen on pre-Montecito.  Even though
> L1D is write-through and L2 was mixed I/D, the L1 I-cache could contain
> stale instrutions if there are missing flushes.

I cannot agree with you.

In order to consider an L1 I-cache entry as valid, a corresponding
virtual -> physic address translation should be valid in one of the L1 ITLBs.

"See 6.1.1. Instruction TLBS" of the I2 Proc. Ref. Man. for SW Dev. & Opt.

You cannot have a valid L1 ITLB entry unless you have a corresponding valid
L2 ITLB entry.

When you remove a PTE (or switch off the exec bit) and you flush the L2 ITLB
matching the old translation (and you kill the corresponding L1 ITLBs),
you do invalidate the corresponding L1 I-cache entries.

Therefore CPU models without split L2 caches are safe.

Thanks,

Zoltan
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