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

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Date:	Thu, 05 Jul 2007 14:29:41 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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.

KAMEZAWA Hiroyuki wrote:
> On Thu, 05 Jul 2007 13:19:41 +1000
> Nick Piggin <nickpiggin@...oo.com.au> wrote:
> 
> 
>>>>>From what I can work out, it is something like "at this point the page
>>>>should be uptodate, so at least the icache won't contain *inconsistent*
>>>>data, just old data which userspace should take care of flushing if it
>>>>modifies". Is that always true?
>>>
>>> 
>>>I think it's true. But, in this case, i-cache doesn't contain *incositent* data.
>>>There are inconsistency between L2-Dcache and L3-mixed-cache. At L2-icache-miss,
>>>a cpu fetches data from L3 cache.
>>>This case seems defficult to be generalized...
>>
>>If there is something in the icache line that isn't the last data to
>>be stored at that address, isn't that inconsistent?
>>
> 
> Hmm..do we have a chance to add do_flush_cache_if_not_filled_by_dma(page)
> before SetPageUptodate(page) ?

Well you shouldn't strictly need to, because only uptodate pages should
ever be mapped with set_pte, and if you do the flush_icache before the
set_pte, then you effectively get the same result.

And if that's the result you want, then I don't think the flush_icache
before set_pte is a *terrible* way to get it.

-- 
SUSE Labs, Novell Inc.
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