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

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Message-ID: <20191105162801.sffoqe2yedrrplnn@ast-mbp.dhcp.thefacebook.com>
Date:   Tue, 5 Nov 2019 08:28:02 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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, 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?

> 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.