linux-kernel - Re: [PATCH V4 3/3] x86: Add entry trampolines to kcore

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Message-ID: <90e24c0c-6ec9-f2c0-54af-0a946b05e574@intel.com>
Date:   Tue, 17 Jul 2018 11:54:30 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>, Jiri Olsa <jolsa@...hat.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH V4 3/3] x86: Add entry trampolines to kcore

On 06/06/18 16:19, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jun 06, 2018 at 03:16:31PM +0200, Peter Zijlstra escreveu:
>> On Wed, Jun 06, 2018 at 03:54:11PM +0300, Adrian Hunter wrote:
>>> Without program headers for PTI entry trampoline pages, the trampoline
>>> virtual addresses do not map to anything.
>>>
>>
>>>
>>> In addition, entry trampolines all map to the same page.  Represent that by
>>> giving the corresponding program headers in kcore the same offset.
>>>
>>> This has the benefit that, when perf tools uses /proc/kcore as a source for
>>> kernel object code, samples from different CPU trampolines are aggregated
>>> together.  Note, such aggregation is normal for profiling i.e. people want
>>> to profile the object code, not every different virtual address the object
>>> code might be mapped to (across different processes for example).
>>>
>>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>>> Acked-by: Andi Kleen <ak@...ux.intel.com>
>>> ---
>>>  arch/x86/mm/cpu_entry_area.c | 10 ++++++++++
>>>  fs/proc/kcore.c              |  7 +++++--
>>>  include/linux/kcore.h        | 13 +++++++++++++
>>>  3 files changed, 28 insertions(+), 2 deletions(-)
>>
>> This also adds the KCORE_REMAP functionality, but isn't mentioned at all
>> in the Changelog.
>>
>> Still, looks OK I suppose,
> 
> I can add a note about that,
>  
>> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> Thanks, giving it some more hours and will apply and try to test it.

Any update on this?