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

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Message-Id: <200704281817.l3SIHu0P001764@smtp.corp.google.com>
Date:	Sat, 28 Apr 2007 11:17:45 -0700
From:	Rohit Seth <rohitseth@...gle.com>
To:	"'Hugh Dickins'" <hugh@...itas.com>
Cc:	"'Nick Piggin'" <nickpiggin@...oo.com.au>,
	"'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

 Hi Hugh,

-----Original Message-----
From: Hugh Dickins [mailto:hugh@...itas.com] 
Sent: Friday, April 27, 2007 10:34 PM
To: Rohit Seth
Cc: Nick Piggin; Mike Stroyan; Andrew Morton; Luck, Tony;
linux-ia64@...r.kernel.org; linux-kernel@...r.kernel.org
Subject: Re: Fw: [PATCH] ia64: race flushing icache in do_no_page path

On Fri, 27 Apr 2007, Rohit Seth wrote:

> lazy_mmu_prot_update was added specifically for notifying change in 
> protection.  So, in a way it is closer to update_mmu_cache (Which is 
> for change in mappings itself).  Though for ia64 implementation, this 
> ends up flushing the icaches when needed.

>The ia64 implementation is the only one which has any use for it, 

Even Itanium didn't need it for almost 5 years :)  Though I think archs that
have incoherent I & D caches could be (theoritically) exposed to same
(original) mprotect code path bug that triggered this API.

>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.

Cheers,
-rohit


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