From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Björn Töpel" <bjorn.topel@gmail.com>,
"Network Development" <netdev@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Björn Töpel" <bjorn.topel@intel.com>, bpf <bpf@vger.kernel.org>,
"Magnus Karlsson" <magnus.karlsson@gmail.com>,
"Karlsson, Magnus" <magnus.karlsson@intel.com>,
"Jonathan Lemon" <jonathan.lemon@gmail.com>,
"Edward Cree" <ecree@solarflare.com>,
"Toke Høiland-Jørgensen" <thoiland@redhat.com>,
"Jesper Dangaard Brouer" <brouer@redhat.com>,
"Andrii Nakryiko" <andrii.nakryiko@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Christoph Hellwig" <hch@infradead.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"Josh Poimboeuf" <jpoimboe@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher
Date: Mon, 15 Aug 2022 08:19:16 -0700 [thread overview]
Message-ID: <CAADnVQKijkstBqV_JhQSaBXZ+65coY+8=UGw8tPi8-boXV=AOQ@mail.gmail.com> (raw)
In-Reply-To: <20220815111658.58d75672@gandalf.local.home>
On Mon, Aug 15, 2022 at 8:16 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Mon, 15 Aug 2022 07:31:23 -0700
> Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > >
> > > When I heard that ftrace was broken by BPF I thought it was something
> > > unique they were doing, but unfortunately, I didn't investigate what they
> > > were doing at the time.
> >
> > ftrace is still broken and refusing to accept the fact doesn't make it
> > non-broken.
>
> I extended Jiri's patch to make it work again.
>
> >
> > > Then they started sending me patches to hide fentry locations from ftrace.
> > > And even telling me that fentry != ftrace
> >
> > It sounds that you've invented nop5 and kernel's ability
> > to replace nop5 with a jump or call.
>
> Actually I did invent it.
>
> https://lore.kernel.org/lkml/20080210072109.GR4100@elte.hu/
>
>
> I'm the one that introduced the code to convert mcount into the 5 byte nop,
> and did the research and development to make it work at run time. I had one
> hiccup along the way that caused the e1000e network card breakage.
>
> The "daemon" approach was horrible, and then I created the recordmcount.pl
> perl script to accomplish the same thing at compile time.
>
> > ftrace should really stop trying to own all of the kernel text rewrites.
> > It's in the way. Like this case.
>
> It's not trying to own all modifications (static_calls is not ftrace). But
> the code at the start of functions with fentry does belong to it.
>
> >
> > > https://lore.kernel.org/all/CAADnVQJTT7h3MniVqdBEU=eLwvJhEKNLSjbUAK4sOrhN=zggCQ@mail.gmail.com/
> > >
> > > Even though fentry was created for ftrace
> > >
> > > https://lore.kernel.org/lkml/1258720459.22249.1018.camel@gandalf.stny.rr.com/
> > >
> > > and all the work with fentry was for the ftrace infrastructure. Ftrace
> > > takes a lot of care for security and use cases for other users (like
> > > live kernel patching). But BPF has the NIH syndrome, and likes to own
> > > everything and recreate the wheel so that they have full control.
> > >
> > > > of the trampoline. One dispatcher instance currently supports up to 64
> > > > dispatch points. A user creates a dispatcher with its corresponding
> > > > trampoline with the DEFINE_BPF_DISPATCHER macro.
> > >
> > > Anyway, this patch just looks like a re-implementation of static_calls:
> >
> > It was implemented long before static_calls made it to the kernel
> > and it's different. Please do your home work.
>
> Long before? This code made it into the kernel in Dec 2019. Yes static calls
> finally made it into the kernel in 2020, but it was first introduced in
> October 2018:
>
> https://lore.kernel.org/all/20181006015110.653946300@goodmis.org/
>
> If you had Cc'd us on this patch, we could have collaborated and come up
> with something that would have worked for you.
>
> It took time to get in because we don't just push our features in, we make
> sure that they are generic and work for others, and is secure and robust.
>
> I sent a proof of concept, Josh took over, Linus had issues, and finally
> Peter pushed it through the gate. It's a long process, but we don't break
> others code while doing it!
Replied in the other thread. Let's stick to one thread please.
next prev parent reply other threads:[~2022-08-15 15:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20191211123017.13212-1-bjorn.topel@gmail.com>
[not found] ` <20191211123017.13212-3-bjorn.topel@gmail.com>
2022-08-15 14:13 ` [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher Steven Rostedt
2022-08-15 14:31 ` Alexei Starovoitov
2022-08-15 14:56 ` Peter Zijlstra
2022-08-15 15:16 ` Steven Rostedt
2022-08-15 15:19 ` Alexei Starovoitov [this message]
2022-08-15 15:21 ` Steven Rostedt
2022-08-15 15:39 ` Steven Rostedt
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