netdev - Re: [PATCH bpf-next 0/7] Introduce BPF trampoline

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Message-ID: <20191105122629.29aecc69@grimm.local.home>
Date:   Tue, 5 Nov 2019 12:26:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net,
        daniel@...earbox.net, peterz@...radead.org, x86@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH bpf-next 0/7] Introduce BPF trampoline

On Tue, 5 Nov 2019 08:28:02 -0800
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Tue, Nov 05, 2019 at 11:00:28AM -0500, Steven Rostedt wrote:
> > On Tue, 5 Nov 2019 07:47:11 -0800
> > Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> >   
> > > > If you have to wait you may need to wait. The Linux kernel isn't
> > > > something that is suppose to put in temporary hacks, just to satisfy
> > > > someone's deadline.    
> > > 
> > > Ok. I will switch to text_poke and will make it hack free.
> > > ftrace mechanisms are being replaced by text_poke anyway.  
> > 
> > I see that Facebook now owns Linux.  
> 
> huh?

Sorry, I'm a bit grumpy. I've been non stop for over a week (7 days of
conferences), and I'm still not done traveling yet. :-p


> 
> > Peter's text poke patches most likely not be ready for the next
> > merge window either. Don't you require them?  
> 
> nope.
> But I strongly support them. ftrace->text_poke + static_call + nop2
> are all great improvements.
> I'd really like to see them landing in this merge window.
> 
> > The database of function nops are part of the ftrace mechanisms which
> > are not part of text poke, and there's strong accounting associated to
> > them which allows the user to see how their kernel is modified.   
> 
> I guess the part that wasn't obvious from commit log of bpf trampoline patches
> is that they don't care about nops and ftrace recording of nops. bpf trampoline
> will work even if there are no nops in front of the function. It will work when
> CONFIG_HAVE_FENTRY is off.

I'm guessing it will use kprobes (or optimized probes). I haven't had a
chance to look at your patches.

I still think using the register_ftrace_direct() will be cleaner (as it
is built on top of code that's been in the kernel for a decade).
Perhaps we can make it work even without the full ftrace code.

-- Steve