From: Frederic Weisbecker <fweisbec@gmail.com>
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 <systemtap@sources.redhat.com>,
DLE <dle-develop@lists.sourceforge.net>,
Jim Keniston <jkenisto@us.ibm.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Christoph Hellwig <hch@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Anders Kaseorg <andersk@ksplice.com>,
Tim Abbott <tabbott@ksplice.com>,
Andi Kleen <andi@firstfloor.org>,
Jason Baron <jbaron@redhat.com>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Subject: Re: [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump optimization on x86
Date: Tue, 24 Nov 2009 03:15:00 -0000 [thread overview]
Message-ID: <20091124031456.GC6752@nowhere> (raw)
In-Reply-To: <20091123232211.22071.58974.stgit@dhcp-100-2-132.bos.redhat.com>
On Mon, Nov 23, 2009 at 06:22:11PM -0500, Masami Hiramatsu wrote:
> Introduce x86 arch-specific optimization code, which supports both of
> x86-32 and x86-64.
>
> This code also supports safety checking, which decodes whole of a function
> in which probe is inserted, and checks following conditions before
> optimization:
> - The optimized instructions which will be replaced by a jump instruction
> don't straddle the function boundary.
> - There is no indirect jump instruction, because it will jumps into
> the address range which is replaced by jump operand.
> - There is no jump/loop instruction which jumps into the address range
> which is replaced by jump operand.
> - Don't optimize kprobes if it is in functions into which fixup code will
> jumps.
>
> This uses stop_machine() for corss modifying code from int3 to jump.
> It doesn't allow us to modify code on NMI/SMI path. However, since
> kprobes itself doesn't support NMI/SMI code probing, it's not a
> problem.
>
> Changes in v5:
> - Introduce stop_machine-based jump replacing.
I realize now that int 3 live patching doesn't need stop_machine().
But still, I don't understand the int 3 unecessary step.
You first force int 3 patching, and later try to optimize
with a jump, using stop_machine().
But why the int 3 is a necessary first step? I guess it was
necessary first when you used it as a gate:
- patch with int 3, go to handler, go to old instruction
that was patched, jump to original code that folows
instruction that was patched
- set up detour buffer, execute handler (from int 3)
then route to detour buffer, and original code that
follows
- the code to be patched with the jump is now a
dead code, jump to it
And now that you use stop_machine(), the complexity could be
reduced to:
- decide kprobe mode
- if int 3, then do like usual
- if jmp, then prepare detour buffer, and patch with the jump,
without worrying about routing int 3 to the detour buffer
to create a dead code area. It is now safe because of stop_machine()
Of course it's possible I completely misunderstood the whole
thing :)
next prev parent reply other threads:[~2009-11-24 3:15 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-23 23:18 [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support Masami Hiramatsu
2009-11-23 23:18 ` [PATCH -tip v5 02/10] kprobes: Introduce generic insn_slot framework Masami Hiramatsu
2009-11-23 23:18 ` [PATCH -tip v5 01/10] kprobes/x86: Cleanup RELATIVEJUMP_INSTRUCTION to RELATIVEJUMP_OPCODE Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 04/10] kprobes: Jump optimization sysctl interface Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 05/10] kprobes/x86: Boost probes when reentering Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump optimization on x86 Masami Hiramatsu
2009-11-24 3:15 ` Frederic Weisbecker [this message]
2009-11-24 16:27 ` Jason Baron
2009-11-24 17:46 ` Masami Hiramatsu
2009-11-25 16:12 ` Masami Hiramatsu
2009-11-24 16:42 ` H. Peter Anvin
2009-11-24 17:01 ` Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump optimization Masami Hiramatsu
2009-11-24 2:44 ` Frederic Weisbecker
2009-11-24 3:31 ` Frederic Weisbecker
2009-11-24 15:32 ` Masami Hiramatsu
2009-11-24 20:14 ` Frederic Weisbecker
2009-11-24 20:59 ` Masami Hiramatsu
2009-11-25 21:09 ` Steven Rostedt
2009-11-25 21:30 ` Masami Hiramatsu
2009-11-24 21:12 ` H. Peter Anvin
2009-11-24 15:31 ` Masami Hiramatsu
2009-11-24 19:45 ` Frederic Weisbecker
2009-11-24 21:15 ` Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 06/10] kprobes/x86: Cleanup save/restore registers Masami Hiramatsu
2009-11-24 2:51 ` Frederic Weisbecker
2009-11-24 15:36 ` Masami Hiramatsu
2009-11-24 20:19 ` Frederic Weisbecker
2009-11-24 15:40 ` Frank Ch. Eigler
2009-11-24 20:20 ` Frederic Weisbecker
2009-11-23 23:19 ` [PATCH -tip v5 10/10] [RFC] kprobes/x86: Use text_poke_fixup() for jump optimization Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 08/10] kprobes: Add documents of " Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 09/10] [RFC] x86: Introduce generic jump patching without stop_machine Masami Hiramatsu
2009-11-24 2:03 ` [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support Frederic Weisbecker
2009-11-24 3:20 ` Frederic Weisbecker
2009-11-24 7:53 ` Ingo Molnar
2009-11-24 16:03 ` Masami Hiramatsu
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