linux-kernel - Re: [PATCH v9 bpf-next 9/9] bpf, x86_64: use bpf_jit_binary_pack

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Message-ID: <20220703031456.rsj4ruqmcr34mnsd@alap3.anarazel.de>
Date:   Sat, 2 Jul 2022 20:14:56 -0700
From:   Andres Freund <andres@...razel.de>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Kernel Team <kernel-team@...com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH v9 bpf-next 9/9] bpf, x86_64: use
 bpf_jit_binary_pack_alloc

Hi,

On 2022-07-02 20:03:56 -0700, Alexei Starovoitov wrote:
> On Sat, Jul 2, 2022 at 8:02 PM Andres Freund <andres@...razel.de> wrote:
> > On 2022-02-04 10:57:42 -0800, Song Liu wrote:
> > > From: Song Liu <songliubraving@...com>
> > >
> > > Use bpf_jit_binary_pack_alloc in x86_64 jit. The jit engine first writes
> > > the program to the rw buffer. When the jit is done, the program is copied
> > > to the final location with bpf_jit_binary_pack_finalize.
> > >
> > > Note that we need to do bpf_tail_call_direct_fixup after finalize.
> > > Therefore, the text_live = false logic in __bpf_arch_text_poke is no
> > > longer needed.
> >
> > I think this broke bpf_jit_enable = 2.
> 
> Good. We need to remove that knob.
> It's been wrong for a long time.

Fine with me - I've never used it before trying to verify I am not breaking
tools/bpf/bpf_jit_disasm...

And yea, it does look like it bpf_jit_dump() was called too early before that
commit as well, just not as consequentially so.

Greetings,

Andres Freund