On Thu, Nov 14, 2019 at 07:23:46PM -0800, Alexei Starovoitov wrote:
> On Fri, Nov 15, 2019 at 02:04:01AM +0100, Daniel Borkmann wrote:
> > for later modifications. In ii) fixup_bpf_tail_call_direct() walks
> > over the progs poke_tab, locks the tail call maps poke_mutex to
> > prevent from parallel updates and patches in the right locations via
> ...
> > @@ -1610,6 +1671,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog)
> > prog->bpf_func = (void *)image;
> > prog->jited = 1;
> > prog->jited_len = proglen;
> > + fixup_bpf_tail_call_direct(prog);
>
> Why not to move fixup_bpf_tail_call_direct() just before
> bpf_jit_binary_lock_ro() and use simple memcpy instead of text_poke ?
Thinking about it, I'll move it right into the branch before we lock ...
if (!prog->is_func || extra_pass) {
bpf_tail_call_fixup_direct(prog);
bpf_jit_binary_lock_ro(header);
} else { [...]
... and I'll add a __bpf_arch_text_poke() handler which passes in the
a plain memcpy() callback instead of text_poke_bp(), so it keeps reusing
most of the logic/checks from __bpf_arch_text_poke() which we also have
at a later point once the program is live.
> imo this logic in patch 7:
> case BPF_JMP | BPF_TAIL_CALL:
> + if (imm32)
> + emit_bpf_tail_call_direct(&bpf_prog->aux->poke_tab[imm32 - 1],
> would have been easier to understand if patch 7 and 8 were swapped.
Makes sense, it's totally fine to swap them, so I'll go do that. Thanks
for the feedback!
Cheers,
Daniel
