From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
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 18:28:42 -0800 [thread overview]
Message-ID: <CAADnVQJqYE5TAdJ=o8nHSF1mXoXpsVNXcJtWSPQJDn7wUvxR=Q@mail.gmail.com> (raw)
In-Reply-To: <ba52688c-49bf-7897-4ba2-f62f30d501a9@iogearbox.net>
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);
Not sure whether it's gonna be any cleaner.
Intuitively doesn't feel so.
next prev parent reply other threads:[~2019-11-23 2:28 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 [this message]
2019-11-23 5:00 ` Andrii Nakryiko
2019-11-23 6:18 ` Alexei Starovoitov
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
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