From: Masami Hiramatsu <mhiramat@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
Ingo Molnar <mingo@elte.hu>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
systemtap-ml <systemtap@sources.redhat.com>
Subject: Re: [BUG][-tip] kprobes on module functions hits kernel BUG in text_poke on x86-32
Date: Sun, 05 Apr 2009 03:45:00 -0000 [thread overview]
Message-ID: <49D82987.5090003@redhat.com> (raw)
In-Reply-To: <49D7AF26.5030808@redhat.com>
Masami Hiramatsu wrote:
> Masami Hiramatsu wrote:
>> Mathieu Desnoyers wrote:
>>> * Masami Hiramatsu (mhiramat@redhat.com) wrote:
>>>> Hi,
>>>>
>>>> I found text_poke() problem on x86-32 with the latest-tip tree.
>>>> When I put a kprobe on a module function, text_poke() hit a BUG.
>>>>
>>>> This bug can be reproduced on x86-32, but not on x86-64.
>>>> And inserting kprobes on a kernel-core function is OK.
>>>>
>>>> Thank you,
>>>>
>>> Hi Masami,
>>>
>>> OK, so text_poke safety net saves the day :)
>>>
>>> Basically, what we have here is the BUG_ON I have put :
>>>
>>> for (i = 0; i < len; i++)
>>> BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
>>>
>>> Which checks that the modification is really preceivable in the kernel
>>> code, triggers this bug. Only for modules you say.
>>>
>>> It might not be this, but.. let's try something simple (this could be
>>> completely unrelated, but won't take long to test): can you try to add a
>>> vmalloc_sync_all() at the beginning of text_poke ? This would make sure
>>> that lazily-populated TLB entries, which include module code and data on
>>> x86, will be populated. I wonder if we hit this problem because
>>> vmalloc_to_page would be returning a mapping to a yet unpopulated TLB
>>> entry, if it is ever possible.
>> Hmm, from the result of my test, vmalloc_sync_all() didn't change anything...
>>
>>> If that's not this, then I guess we have some problem with setting a
>>> fixmap to a page returned by vmalloc on x86 32.
Hmm, ok. AFAICS, fixmap is only for lowmem, and pkmap is only for highmem.
So, I think we have some options;
A) Separate text_poke into __text_poke and __text_poke_highmem. And
use pkmap_atomic in __text_poke_highmem. This way doesn't require
any additional change except adding KM_TEXT_POKE0/1 in km_type.
B) Add set_fixmap_page and use it in text_poke. This will require
changes in paravirt_ops and pgtable.c. We need to ensure there is
no side effects.
C) Change pkmap_atomic_prot to map lowmem only if the page's pgprot
is different from user specified pgprot. And use it instead of
fixmap. This also requires KM_TEXT_POKE0/1, however we can
remove FIX_TEXT_POKE0/1.
etc...
I think A) is for short-term solution. I guess it will be acceptable
for next release. But for long-term, C) might be better.
Thank you,
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com
next prev parent reply other threads:[~2009-04-05 3:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-04 14:34 Masami Hiramatsu
2009-04-04 15:42 ` Mathieu Desnoyers
2009-04-04 18:28 ` Masami Hiramatsu
2009-04-04 19:03 ` Masami Hiramatsu
2009-04-05 3:45 ` Masami Hiramatsu [this message]
2009-04-05 3:49 ` Masami Hiramatsu
2009-04-06 17:10 ` [BUGFIX][PATCH -tip] x86: fix text_poke to handle highmem pages Masami Hiramatsu
2009-04-06 17:32 ` Mathieu Desnoyers
2009-04-06 17:43 ` Masami Hiramatsu
2009-04-06 17:58 ` Mathieu Desnoyers
2009-04-06 20:22 ` Masami Hiramatsu
2009-04-08 12:33 ` Ingo Molnar
2009-04-08 14:57 ` Masami Hiramatsu
2009-04-08 15:00 ` 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 21:51 ` Masami Hiramatsu
2009-04-10 14:09 ` [tip:x86/urgent] " Masami Hiramatsu
2009-04-10 15:20 ` Masami Hiramatsu
2009-04-10 16:11 ` Mathieu Desnoyers
2009-04-10 17:48 ` Masami Hiramatsu
2009-04-10 18:32 ` Masami Hiramatsu
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