linux-kernel - Re: Fw: [PATCH] ia64: race flushing icache in do_no

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Date:	Wed, 02 May 2007 12:05:15 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	rohitseth@...gle.com
CC:	'Hugh Dickins' <hugh@...itas.com>,
	'Mike Stroyan' <mike.stroyan@...com>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	"'Luck, Tony'" <tony.luck@...el.com>, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Fw: [PATCH] ia64: race flushing icache in do_no_page path

Rohit Seth wrote:
> On Tue, 2007-05-01 at 21:52 +1000, Nick Piggin wrote:
> 
>>Rohit Seth wrote:
>>
>>
>>>>and 
>>>>it's only interested when it's executable i.e. "lazy_mmu_prot_update"
>>>>is a name concealing some overdesign.
>>>
>>>
>>>You are right that ia64 is only interested in whne the execute permissions
>>>kick in (and FWIW ia64 used to use update_mmu_cache API to do what it is now
>>>doing lazy_mmu_prot_update).  Though the idea was to design an API that any
>>>arch can use to know when ever there is change in protections on a mapping.
>>
>>What I think what we should do is audit flush_icache_page coverage, and
>>convert ia64 to use that (because it needs this to happen _before_ the
>>pte is set).
>>
> 
> 
> That doesn't address the underlying requirement that arch specific code
> should be told of change in protections. 

But you would add the flush_icache_page_chprot to address that.


> For ia64, you are right that
> it equates to flushing icache in some cases, but this API is more
> generic.

And it is also broken, because it needs to be done before the set_pte
for ia64. It needs to be done where flush_icache_page is done. And on
ia64 it flushes the icache. So I don't understand why ia64 would not
use flush_icache_page but add something completely new "because it is
more generic".


>>All we should need to do is add a pte argument to flush_icache,
> 
> 
> I'm sure this is doable.  Though it is more of design issue of whether
> that is the right way to do it.  I understand this extra API is
> difficult at this time because of one single consumer.

There is just no point in adding something else if you already have
a hook that seems to do what ia64 wants (or could, with a small amount
of work).

-- 
SUSE Labs, Novell Inc.
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