Subject: Re: [PATCH v2 0/2] Stop Intel Processor Trace logging on panic
To: <tglx@linutronix.de>, <mingo@redhat.com>, <hpa@zytor.com>,
        <a.p.zijlstra@chello.nl>, <acme@kernel.org>,
        <alexander.shishkin@linux.intel.com>, <vgoyal@redhat.com>
References: <1446614553-6072-1-git-send-email-indou.takao@jp.fujitsu.com>
CC: <linux-kernel@vger.kernel.org>, <x86@kernel.org>
From: Takao Indoh <indou.takao@jp.fujitsu.com>
Message-ID: <56448077.8090706@jp.fujitsu.com>
Date: Thu, 12 Nov 2015 21:05:11 +0900
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Ping, any comments on these patches?

Thanks,
Takao Indoh

On 2015/11/04 14:22, Takao Indoh wrote:
> Hi all,
> 
> These patch series provide a feature to stop Intel Processor Trace
> (Intel PT) logging and save its registers in the memory on panic.
> 
> Intel PT is a new feature of Intel CPU "Broadwell", it captures
> information about program execution flow. Here is a article about Intel
> PT.
> https://software.intel.com/en-us/blogs/2013/09/18/processor-tracing
> 
> Once Intel PT is enabled, the events which change program flow, like
> branch instructions, exceptions, interruptions, traps and so on are
> logged in the memory. This is very useful for debugging because we can
> know the detailed behavior of software.
> 
> When kernel panic occurs while you are running a perf command with Intel
> PT (with -e intel_pt// option), these patches disable Intel PT and save
> its registers in the memory. After crash dump is captured by kdump, you
> can retrieve Intel PT log buffer from vmcore and investigate kernel
> behavior. I have not made a tool yet to salvage Intel PT log buffer from
> vmcore, but I'll do once these patches are accepted.
> 
> changelog:
> v2:
> - Define function in intel_pt.h with static inline
> 
> v1:
> https://lkml.org/lkml/2015/10/28/136
> 
> 
> Background:
> These patches are a part of patch series I posted before, the original
> discussion is bellow.
> 
> x86: Intel Processor Trace Logger
> v1: https://lkml.org/lkml/2015/7/29/6
> v2: https://lkml.org/lkml/2015/9/8/24
> 
> The purpose of the original patches is introducing in-kernel logger
> using Intel PT. To implement it I need to add some APIs to control perf
> counter and ring buffer in kernel. Alexander Shishkin is working on such
> APIs for his work to make use of Intel PT for process core dump. Apart
> from such APIs, the feature to save Intel PT registers on panic is
> helpful for normal perf command user as I described above, therefore I
> separate the feature from original patches.
> 
> Takao Indoh (2):
>    perf/x86/intel/pt: Add interface to stop Intel PT logging
>    x86: Stop Intel PT before kdump starts
> 
>   arch/x86/include/asm/intel_pt.h           |   10 ++++++++++
>   arch/x86/kernel/cpu/perf_event_intel_pt.c |    9 +++++++++
>   arch/x86/kernel/crash.c                   |   11 +++++++++++
>   3 files changed, 30 insertions(+), 0 deletions(-)
>   create mode 100644 arch/x86/include/asm/intel_pt.h
> 
> 
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