linux-kernel - Re: [BUGFIX][PATCH] DO flush icache before set

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Date:	Wed, 4 Jul 2007 16:38:26 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Christoph Lameter <clameter@....com>, Mike.stroya@...com,
	GOTO <y-goto@...fujitsu.com>, dmosberger@...il.com,
	hugh@...itas.com
Subject: Re: [BUGFIX][PATCH] DO flush icache before set_pte() on ia64.

On Wed, 04 Jul 2007 16:31:06 +1000
Nick Piggin <nickpiggin@...oo.com.au> wrote:
> The only thing I noticed when I looked at the code is that some places
> may not have flushed icache when they should have? Did you get them all?

I think that I added flush_icache_page() to the place where any flush_(i)cache_xxx
is not called and lazy_mmu_prot_update was used instead of them.
But I want good review, of course.

> Minor nitpick: you have one place where you test VM_EXEC before flushing,
> but the flush routine itself contains the same test I think?
> 
Ah, yes...in do_anonymous_page(). my mistake.

> Regarding the ia64 code -- I'm not an expert so I can't say whether it
> is the right thing to do or not. However I still can't work out what it's
> rationale for the PG_arch_1 bit is, exactly. Does it assume that
> flush_dcache_page sites would only ever be encountered by pages that are
> not faulted in? A faulted in page kind of is "special" because it is
> guaranteed uptodate, but is the ia64 arch code relying on that? Should it?

(I'm sorry if I misses point.)
ia64's D-cache is coherent but I-cache and D-cache is not coherent and any
invalidation against d-cache will invalidate I-cache.

In my understanding :
PG_arch_1 is used for showing "there is no inconsistent data on any level of
cache". PG_uptodate is used for showing "this page includes the newest data
and contents are valid."
...maybe not used for the same purpose.

BTW, a page filled by DMA should have PG_arch_1 :(

-Kame

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