linux-kernel - Re: [BUGFIX][PATCH -tip] x86: fix text

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Date:	Mon, 06 Apr 2009 13:44:37 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: [BUGFIX][PATCH -tip] x86: fix text_poke to handle highmem pages

Mathieu Desnoyers wrote:
> * Masami Hiramatsu (mhiramat@...hat.com) wrote:
>> Fix a bug in text_poke to handle highmem pages, because module
>> text pages are possible to be highmem pages on x86-32.
>> In that case, since fixmap can't handle those pages, text_poke
>> uses kmap_atomic.
>>
> 
> Hrm, can you remind me what would be the downside of using kmap_atomic
> in every scenarios (highmem and non-highmem) then ?

kmap_atomic can handle only highmem pages. If you passes lowmem pages,
it returns just original vaddr of it. (because kmap is only for
highmem support)

> 
> I would try to avoid "special cases" as much as possible, because they
> just make problems harder to reproduce.

Actually, this bug is a special case because it happens only on PAE kernel.

> 
> The idea would be to either add fixmap highmem support, or to simply use
> kmap_atomic() for all cases until we add fixmap highmem support.
> 


Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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