From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
systemtap-ml <systemtap@sources.redhat.com>
Subject: Re: [BUGFIX][PATCH -tip] x86: fix text_poke to handle highmem pages
Date: Mon, 6 Apr 2009 13:58:07 -0400 [thread overview]
Message-ID: <20090406175807.GD31867@Krystal> (raw)
In-Reply-To: <49DA3F85.7050302@redhat.com>
* Masami Hiramatsu (mhiramat@redhat.com) wrote:
> Mathieu Desnoyers wrote:
> > * Masami Hiramatsu (mhiramat@redhat.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)
>
OK, and if we are doing a second kmap_atomic() of a module text page
which is already mapped, does the second kmap_atomic return the vaddr of
the page originally mapped or is it creating a second mapping ?
Because if we ever decide to enforce read-only page mapping for module
text pages, touching highmem pages too, we will run into real trouble if
those happen to be the same page.
Mathieu
> >
> > 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@redhat.com
>
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
next prev parent reply other threads:[~2009-04-06 17:59 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-04 14:34 [BUG][-tip] kprobes on module functions hits kernel BUG in text_poke on x86-32 Masami Hiramatsu
2009-04-04 15:42 ` Mathieu Desnoyers
2009-04-04 18:28 ` Masami Hiramatsu
2009-04-04 19:04 ` Masami Hiramatsu
2009-04-05 3:46 ` Masami Hiramatsu
2009-04-05 3:49 ` Masami Hiramatsu
2009-04-06 17:11 ` [BUGFIX][PATCH -tip] x86: fix text_poke to handle highmem pages Masami Hiramatsu
2009-04-06 17:32 ` Mathieu Desnoyers
2009-04-06 17:44 ` Masami Hiramatsu
2009-04-06 17:58 ` Mathieu Desnoyers [this message]
2009-04-06 20:23 ` Masami Hiramatsu
2009-04-08 12:31 ` Ingo Molnar
2009-04-08 14:57 ` Masami Hiramatsu
2009-04-08 14:59 ` Ingo Molnar
2009-04-09 17:55 ` [BUGFIX][PATCH] x86: fix set_fixmap to use phys_addr_t Masami Hiramatsu
2009-04-09 18:46 ` Mathieu Desnoyers
2009-04-09 21:52 ` Masami Hiramatsu
2009-04-10 14:06 ` [tip:x86/urgent] " Masami Hiramatsu
2009-04-10 15:20 ` Masami Hiramatsu
2009-04-10 16:05 ` Mathieu Desnoyers
2009-04-10 17:48 ` Masami Hiramatsu
2009-04-10 18:30 ` Masami Hiramatsu
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