netdev - Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog load/unload

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Message-ID: <20180920133628.GQ24142@hirez.programming.kicks-ass.net>
Date:   Thu, 20 Sep 2018 15:36:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>, daniel@...earbox.net,
        acme@...nel.org, netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 2/3] bpf: emit RECORD_MMAP events for bpf prog
 load/unload

On Thu, Sep 20, 2018 at 10:44:24AM +0200, Peter Zijlstra wrote:
> On Wed, Sep 19, 2018 at 03:39:34PM -0700, Alexei Starovoitov wrote:
> >  void bpf_prog_kallsyms_del(struct bpf_prog *fp)
> >  {
> > +	unsigned long symbol_start, symbol_end;
> > +	/* mmap_record.filename cannot be NULL and has to be u64 aligned */
> > +	char buf[sizeof(u64)] = {};
> > +
> >  	if (!bpf_prog_kallsyms_candidate(fp))
> >  		return;
> >  
> >  	spin_lock_bh(&bpf_lock);
> >  	bpf_prog_ksym_node_del(fp->aux);
> >  	spin_unlock_bh(&bpf_lock);
> > +	bpf_get_prog_addr_region(fp, &symbol_start, &symbol_end);
> > +	perf_event_mmap_bpf_prog(symbol_start, symbol_end - symbol_start,
> > +				 buf, sizeof(buf));
> >  }
> 
> So perf doesn't normally issue unmap events.. We've talked about doing
> that, but so far it's never really need needed I think.
> 
> I feels a bit weird to start issuing unmap events for this.

FWIW:

  https://lkml.kernel.org/r/20170127130702.GI6515@twins.programming.kicks-ass.net

has talk of PERF_RECORD_MUNMAP