From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Cc: "Daniel Borkmann" <daniel@iogearbox.net>,
"Alexei Starovoitov" <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
"Network Development" <netdev@vger.kernel.org>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Karlsson, Magnus" <magnus.karlsson@intel.com>
Subject: Re: [PATCH bpf-next 4/5] bpf, x64: rework pro/epilogue and tailcall handling in JIT
Date: Fri, 17 Jul 2020 09:16:27 -0700 [thread overview]
Message-ID: <CAADnVQLz0ojicbKS4LSjCCb5yaK9xKzB0MEJNYzb+Z6bVAFt4g@mail.gmail.com> (raw)
In-Reply-To: <20200717105744.GB11239@ranger.igk.intel.com>
On Fri, Jul 17, 2020 at 4:02 AM Maciej Fijalkowski
<maciej.fijalkowski@intel.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.
next prev parent reply other threads:[~2020-07-17 16:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-15 23:36 [PATCH bpf-next 0/5] bpf: tailcalls in BPF subprograms Maciej Fijalkowski
2020-07-15 23:36 ` [PATCH bpf-next 1/5] bpf, x64: use %rcx instead of %rax for tail call retpolines Maciej Fijalkowski
2020-07-16 20:36 ` Daniel Borkmann
2020-07-17 9:29 ` Maciej Fijalkowski
2020-07-15 23:36 ` [PATCH bpf-next 2/5] bpf: allow for tailcalls in BPF subprograms Maciej Fijalkowski
2020-07-16 21:10 ` Daniel Borkmann
2020-07-16 21:29 ` Daniel Borkmann
2020-07-16 22:46 ` Daniel Borkmann
2020-07-17 11:39 ` Maciej Fijalkowski
2020-07-15 23:36 ` [PATCH bpf-next 3/5] bpf: propagate poke descriptors to subprograms Maciej Fijalkowski
2020-07-16 21:16 ` Daniel Borkmann
2020-07-17 9:36 ` Maciej Fijalkowski
2020-07-15 23:36 ` [PATCH bpf-next 4/5] bpf, x64: rework pro/epilogue and tailcall handling in JIT Maciej Fijalkowski
2020-07-16 23:06 ` Daniel Borkmann
2020-07-17 2:16 ` Alexei Starovoitov
2020-07-17 10:57 ` Maciej Fijalkowski
2020-07-17 16:16 ` Alexei Starovoitov [this message]
2020-07-17 10:52 ` Maciej Fijalkowski
2020-07-15 23:36 ` [PATCH bpf-next 5/5] selftests: bpf: add dummy prog for bpf2bpf with tailcall Maciej Fijalkowski
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