From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
john fastabend <john.fastabend@gmail.com>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH bpf-next v2 7/8] bpf, x86: emit patchable direct jump as tail call
Date: Fri, 22 Nov 2019 22:18:07 -0800 [thread overview]
Message-ID: <20191123061805.grankibnqpae4tnd@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAEf4BzZS-yAfYXruzG5+_Wh0Ob4-ChPMPuhcDx4zDoGwUQygcA@mail.gmail.com>
On Fri, Nov 22, 2019 at 09:00:35PM -0800, Andrii Nakryiko wrote:
> On Fri, Nov 22, 2019 at 6:28 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Fri, Nov 22, 2019 at 3:25 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
> > > >> + case BPF_MOD_CALL_TO_NOP:
> > > >> + case BPF_MOD_JUMP_TO_NOP:
> > > >> + if (old_addr && !new_addr) {
> > > >> + memcpy(new_insn, nop_insn, X86_PATCH_SIZE);
> > > >> +
> > > >> + prog = old_insn;
> > > >> + ret = emit_patch_fn(&prog, old_addr, ip);
> > > >> + if (ret)
> > > >> + return ret;
> > > >> + break;
> > > >> + }
> > > >> + return -ENXIO;
> > > >> + default:
> > > >
> > > > There is this redundancy between BPF_MOD_xxx enums and
> > > > old_addr+new_addr (both encode what kind of transition it is), which
> > > > leads to this cumbersome logic. Would it be simpler to have
> > > > old_addr/new_addr determine whether it's X-to-NOP, NOP-to-Y, or X-to-Y
> > > > transition, while separate bool or simple BPF_MOD_CALL/BPF_MOD_JUMP
> > > > enum determining whether it's a call or a jump that we want to update.
> > > > Seems like that should be a simpler interface overall and cleaner
> > > > implementation?
> > >
> > > Right we can probably simplify it further, I kept preserving the original
> > > switch from Alexei's code where my assumption was that having the transition
> > > explicitly spelled out was preferred in here and then based on that doing
> > > the sanity checks to make sure we don't get bad input from any call-site
> > > since we're modifying kernel text, e.g. in the bpf_trampoline_update() as
> > > one example the BPF_MOD_* is a fixed constant input there.
> >
> > I guess we can try adding one more argument
> > bpf_arch_text_poke(ip, BPF_MOD_NOP, old_addr, BPF_MOD_INTO_CALL, new_addr);
>
> I was thinking along the lines of:
>
> bpf_arch_text_poke(ip, BPF_MOD_CALL (or BPF_MOD_JMP), old_addr, new_addr);
>
> old_addr/new_addr being possibly NULL determine NOP/not-a-NOP.
I see. Something like:
if (BPF_MOD_CALL) {
if (old_addr)
memcmp(ip, old_call_insn);
else
memcmp(ip, nop_insn);
} else if (BPF_MOD_JMP) {
if (old_addr)
memcmp(ip, old_jmp_insn);
else
memcmp(ip, nop_insn);
}
I guess that can work.
next prev parent reply other threads:[~2019-11-23 6:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-22 20:07 [PATCH bpf-next v2 0/8] Optimize BPF tail calls for direct jumps Daniel Borkmann
2019-11-22 20:07 ` [PATCH bpf-next v2 1/8] bpf, x86: generalize and extend bpf_arch_text_poke " Daniel Borkmann
2019-11-22 20:07 ` [PATCH bpf-next v2 2/8] bpf: move bpf_free_used_maps into sleepable section Daniel Borkmann
2019-11-22 20:07 ` [PATCH bpf-next v2 3/8] bpf: move owner type,jited info into array auxiliary data Daniel Borkmann
2019-11-22 20:07 ` [PATCH bpf-next v2 4/8] bpf: add initial poke descriptor table for jit images Daniel Borkmann
2019-11-22 20:07 ` [PATCH bpf-next v2 5/8] bpf: add poke dependency tracking for prog array maps Daniel Borkmann
2019-11-22 22:55 ` Andrii Nakryiko
2019-11-22 23:06 ` Daniel Borkmann
2019-11-22 23:10 ` Andrii Nakryiko
2019-11-22 20:07 ` [PATCH bpf-next v2 6/8] bpf: constant map key tracking for prog array pokes Daniel Borkmann
2019-11-22 22:57 ` Andrii Nakryiko
2019-11-23 10:39 ` Jakub Sitnicki
2019-11-22 20:08 ` [PATCH bpf-next v2 7/8] bpf, x86: emit patchable direct jump as tail call Daniel Borkmann
2019-11-22 23:09 ` Andrii Nakryiko
2019-11-22 23:25 ` Daniel Borkmann
2019-11-23 2:28 ` Alexei Starovoitov
2019-11-23 5:00 ` Andrii Nakryiko
2019-11-23 6:18 ` Alexei Starovoitov [this message]
2019-11-23 9:24 ` Daniel Borkmann
2019-11-22 20:08 ` [PATCH bpf-next v2 8/8] bpf, testing: add various tail call test cases Daniel Borkmann
2019-11-22 23:14 ` Andrii Nakryiko
2019-11-23 2:22 ` [PATCH bpf-next v2 0/8] Optimize BPF tail calls for direct jumps Alexei Starovoitov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191123061805.grankibnqpae4tnd@ast-mbp.dhcp.thefacebook.com \
--to=alexei.starovoitov@gmail.com \
--cc=andrii.nakryiko@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=john.fastabend@gmail.com \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).