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Date: Fri, 17 Jul 2020 09:16:27 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Maciej Fijalkowski <maciej.fijalkowski@...el.com> Cc: Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, Björn Töpel <bjorn.topel@...el.com>, "Karlsson, Magnus" <magnus.karlsson@...el.com> Subject: Re: [PATCH bpf-next 4/5] bpf, x64: rework pro/epilogue and tailcall handling in JIT On Fri, Jul 17, 2020 at 4:02 AM Maciej Fijalkowski <maciej.fijalkowski@...el.com> wrote: > > On Thu, Jul 16, 2020 at 07:16:24PM -0700, Alexei Starovoitov wrote: > > On Fri, Jul 17, 2020 at 01:06:07AM +0200, Daniel Borkmann wrote: > > > > + ret = bpf_arch_text_poke(poke->tailcall_bypass, > > > > + BPF_MOD_JUMP, > > > > + NULL, bypass_addr); > > > > + BUG_ON(ret < 0 && ret != -EINVAL); > > > > + /* let other CPUs finish the execution of program > > > > + * so that it will not possible to expose them > > > > + * to invalid nop, stack unwind, nop state > > > > + */ > > > > + synchronize_rcu(); > > > > > > Very heavyweight that we need to potentially call this /multiple/ times for just a > > > /single/ map update under poke mutex even ... but agree it's needed here to avoid > > > racing. :( > > > > Yeah. I wasn't clear with my suggestion earlier. > > I meant to say that synchronize_rcu() can be done between two loops. > > list_for_each_entry(elem, &aux->poke_progs, list) > > for (i = 0; i < elem->aux->size_poke_tab; i++) > > bpf_arch_text_poke(poke->tailcall_bypass, ... > > synchronize_rcu(); > > list_for_each_entry(elem, &aux->poke_progs, list) > > for (i = 0; i < elem->aux->size_poke_tab; i++) > > bpf_arch_text_poke(poke->poke->tailcall_target, ... > > > > Not sure how much better it will be though. > > text_poke is heavy. > > I think it's heavier than synchronize_rcu(). > > Long term we can do batch of text_poke-s. > > Yeah since we introduce another poke target we could come up with > preparing the vector of pokes as you're saying? yes. eventually. Pls keep it simple for now. The logic is already quite complex.
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