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

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Message-ID: <20180717144735.GA3614@kernel.org>
Date:   Tue, 17 Jul 2018 10:47:35 -0400
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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 Tue, Jul 17, 2018 at 11:54:30AM +0300, Adrian Hunter escreveu:
> 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?

On the post-vacation pile, will get to it.

- Arnaldo