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

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Date:   Wed, 6 Jun 2018 10:19:46 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        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

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.

- Arnaldo