linux-kernel - Re: [PATCH 06/12] perf tools: Do not erase uncovered maps by kcore

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Date:   Tue, 23 Apr 2019 16:55:08 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andi Kleen <ak@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 06/12] perf tools: Do not erase uncovered maps by kcore

On Tue, Apr 23, 2019 at 12:32:12PM +0300, Adrian Hunter wrote:
> On 16/04/19 7:01 PM, Jiri Olsa wrote:
> > Maps in kcore do not cover bpf maps, so we can't just
> > remove everything. Keeping all kernel maps, which are
> > not covered by kcore maps.
> 
> Memory for jited-bpf is allocated from the same area that is used for
> modules.  In the case of /proc/kcore, that entire area is mapped, so there
> won't be any bpf-maps that are not covered.  For copies of kcore made by
> 'perf buildid-cache' the same would be true for any bpf that got allocated
> in between modules.
> 
> But shouldn't the bpf map supersede the kcore map for the address range that
> it maps?  I guess that would mean splitting the kcore map, truncating the
> first piece and inserting the bpf map in between.

I haven't considered it could get in between modules,
I think you're right and we need to cut kcore maps
in case bpf is mapped within.. I'll submit new version

thanks,
jirka

> 
> > 
> > Link: http://lkml.kernel.org/n/tip-9eytka8wofp0a047ul6lmejk@git.kernel.org
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/perf/util/symbol.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index 5cbad55cd99d..96738a7a8c14 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -1166,6 +1166,18 @@ static int kcore_mapfn(u64 start, u64 len, u64 pgoff, void *data)
> >  	return 0;
> >  }
> >  
> > +static bool in_kcore(struct kcore_mapfn_data *md, struct map *map)
> > +{
> > +	struct map *iter;
> > +
> > +	list_for_each_entry(iter, &md->maps, node) {
> > +		if ((map->start >= iter->start) && (map->start < iter->end))
> > +			return true;
> > +	}
> > +
> > +	return false;
> > +}
> > +
> >  static int dso__load_kcore(struct dso *dso, struct map *map,
> >  			   const char *kallsyms_filename)
> >  {
> > @@ -1222,7 +1234,7 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
> >  	while (old_map) {
> >  		struct map *next = map_groups__next(old_map);
> >  
> > -		if (old_map != map)
> > +		if (old_map != map && !in_kcore(&md, old_map))
> >  			map_groups__remove(kmaps, old_map);
> >  		old_map = next;
> >  	}
> > 
>