From: "tiejun.chen" <tiejun.chen@windriver•com>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: Scott Wood <scottwood@freescale•com>,
"linuxppc-dev@ozlabs•org" <linuxppc-dev@ozlabs•org>
Subject: Re: [v3 PATCH 1/1] booke/kprobe: make program exception to use one dedicated exception stack
Date: Wed, 31 Aug 2011 17:17:53 +0800 [thread overview]
Message-ID: <4E5DFC41.7030606@windriver.com> (raw)
In-Reply-To: <1314683064.2488.76.camel@pasglop>
Benjamin Herrenschmidt wrote:
>>> As I understand it, the problem comes from the fact that stwu combines the
>>> creation of a stack frame with storing into that stack frame. If they were
>> Yes.
>>
>>> separate instructions you'd have a new exception frame at a lower address
>>> by the time you actually store to the non-exception frame.
>> So when kprobe we should use a unique stack frame to skip that stack frame the
>> kprobed stwu want to create.
>
> I still don't like that patch. Potentially the problem exist for all
> variants of powerpc, not just booke, and I'm not sure I like adding yet
Yes.
> another exception stack.
But I think we should extend easily this for other powerpc variants. And only
when enable CONFIG_KPROBES that dedicated exception stack is valid, so its not
such a big risk :)
>
> Another (non-great) approach would be to special case stwu to the stack,
> and instead of doing the store while emulating the instruction, keep the
> store address around and do it later, after the stack has been unwound,
> in the exit path (a TIF flag to hit the slow path and then do it in the
> slow path).
Actually I also considered one idea that we do stw-update in the exit path like
your proposal. But I'm not sure if its worth intruding a new TIF flag only for
'stwu'. And if I understand what your exit path means properly, we should do
this on ret_from_except_full,
...
exc_exit_restart:
lwz r11,_NIP(r1)
lwz r12,_MSR(r1)
Looks we have to add something to update as 'stwu' since _NIP/_MSR are also
corrupted potentially. So I feel we'll make this complicated if we really do here.
exc_exit_start:
mtspr SPRN_SRR0,r11
mtspr SPRN_SRR1,r12
REST_2GPRS(11, r1)
lwz r1,GPR1(r1)
.globl exc_exit_restart_end
exc_exit_restart_end:
PPC405_ERR77_SYNC
rfi
b . /* prevent prefetch past rfi */
If I'm wrong please correct me.
>
> It sounds hackish but it makes it easier to fix everybody at once, there
> are "issues" with changing stacks especially on ppc64 and it would
> definitely be affected as well if the stack frame created is larger than
> our gap.
If we provide another exception stack like we did debug exception on ppc64, are
there those "issues" you said?
Thanks
Tiejun
>
> Cheers,
> Ben.
>
>
next prev parent reply other threads:[~2011-08-31 9:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-11 11:31 [v3 PATCH 1/1] booke/kprobe: make program exception to use one dedicated exception stack Tiejun Chen
2011-07-11 11:31 ` [v3] booke/kprobe: Fix stack corrupt issue when kprobe 'stwu' Tiejun Chen
2011-07-14 11:56 ` tiejun.chen
2011-07-12 2:35 ` [v3 PATCH 1/1] booke/kprobe: make program exception to use one dedicated exception stack tiejun.chen
2011-07-14 13:27 ` Kumar Gala
2011-07-14 15:53 ` Scott Wood
2011-07-15 5:28 ` tiejun.chen
2011-07-15 18:42 ` Scott Wood
2011-07-16 3:25 ` Chen, Tiejun
2011-07-18 15:56 ` Scott Wood
2011-07-19 10:52 ` tiejun.chen
2011-08-30 5:44 ` Benjamin Herrenschmidt
2011-08-31 9:17 ` tiejun.chen [this message]
2011-08-31 21:32 ` Benjamin Herrenschmidt
2011-07-21 9:32 ` tiejun.chen
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