linux-kernel - Re: [v4,1/2] arch/powerpc: Implement Optprobes

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Message-Id: <584d290d-e571-5ade-c239-563cb0440704@linux.vnet.ibm.com>
Date:   Wed, 15 Feb 2017 10:44:18 +0530
From:   Anju T Sudhakar <anju@...ux.vnet.ibm.com>
To:     Michael Ellerman <patch-notifications@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     ananth@...ibm.com, mahesh@...ux.vnet.ibm.com, paulus@...ba.org,
        mhiramat@...nel.org, naveen.n.rao@...ux.vnet.ibm.com,
        hemant@...ux.vnet.ibm.com, srikar@...ux.vnet.ibm.com
Subject: Re: [v4,1/2] arch/powerpc: Implement Optprobes

Thank You Michael.  :)


On Tuesday 14 February 2017 06:10 PM, Michael Ellerman wrote:
> On Wed, 2017-02-08 at 09:50:51 UTC, Anju T wrote:
>> Current infrastructure of kprobe uses the unconditional trap instruction
>> to probe a running kernel. Optprobe allows kprobe to replace the trap with
>> a branch instruction to a detour buffer. Detour buffer contains instructions
>> to create an in memory pt_regs. Detour buffer also has a call to
>> optimized_callback() which in turn call the pre_handler().
>> After the execution of the pre-handler, a call is made for instruction
>> emulation. The NIP is determined in advanced through dummy instruction
>> emulation and a branch instruction is created to the NIP at the end of
>> the trampoline.
>>
>> To address the limitation of branch instruction in POWER architecture,
>> detour buffer slot is allocated from a reserved area. For the time being,
>> 64KB is reserved in memory for this purpose.
>>
>> Instructions which can be emulated using analyse_instr() are the candidates
>> for optimization. Before optimization ensure that the address range
>> between the detour buffer allocated and the instruction being probed
>> is within +/- 32MB.
>>
>> Signed-off-by: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
>> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> Series applied to powerpc next, thanks.
>
> https://git.kernel.org/powerpc/c/51c9c0843993528bffc920c54c2121
>
> cheers
>