Re: [PATCH bpf-next v6 0/4] bpf trampoline for arm64

[KP Singh <kpsingh@kernel.org>]

On Tue, Jul 5, 2022 at 6:00 PM Will Deacon <will@kernel.org> wrote:
>
> Hi Daniel,
>
> On Thu, Jun 30, 2022 at 11:12:54PM +0200, Daniel Borkmann wrote:
> > On 6/25/22 6:12 PM, Xu Kuohai wrote:
> > > This patchset introduces bpf trampoline on arm64. A bpf trampoline converts
> > > native calling convention to bpf calling convention and is used to implement
> > > various bpf features, such as fentry, fexit, fmod_ret and struct_ops.
> > >
> > > The trampoline introduced does essentially the same thing as the bpf
> > > trampoline does on x86.
> > >
> > > Tested on raspberry pi 4b and qemu:
> > >
> > >   #18 /1     bpf_tcp_ca/dctcp:OK
> > >   #18 /2     bpf_tcp_ca/cubic:OK
> > >   #18 /3     bpf_tcp_ca/invalid_license:OK
> > >   #18 /4     bpf_tcp_ca/dctcp_fallback:OK
> > >   #18 /5     bpf_tcp_ca/rel_setsockopt:OK
> > >   #18        bpf_tcp_ca:OK
> > >   #51 /1     dummy_st_ops/dummy_st_ops_attach:OK
> > >   #51 /2     dummy_st_ops/dummy_init_ret_value:OK
> > >   #51 /3     dummy_st_ops/dummy_init_ptr_arg:OK
> > >   #51 /4     dummy_st_ops/dummy_multiple_args:OK
> > >   #51        dummy_st_ops:OK
> > >   #57 /1     fexit_bpf2bpf/target_no_callees:OK
> > >   #57 /2     fexit_bpf2bpf/target_yes_callees:OK
> > >   #57 /3     fexit_bpf2bpf/func_replace:OK
> > >   #57 /4     fexit_bpf2bpf/func_replace_verify:OK
> > >   #57 /5     fexit_bpf2bpf/func_sockmap_update:OK
> > >   #57 /6     fexit_bpf2bpf/func_replace_return_code:OK
> > >   #57 /7     fexit_bpf2bpf/func_map_prog_compatibility:OK
> > >   #57 /8     fexit_bpf2bpf/func_replace_multi:OK
> > >   #57 /9     fexit_bpf2bpf/fmod_ret_freplace:OK
> > >   #57        fexit_bpf2bpf:OK
> > >   #237       xdp_bpf2bpf:OK
> > >
> > > v6:
> > > - Since Mark is refactoring arm64 ftrace to support long jump and reduce the
> > >    ftrace trampoline overhead, it's not clear how we'll attach bpf trampoline
> > >    to regular kernel functions, so remove ftrace related patches for now.
> > > - Add long jump support for attaching bpf trampoline to bpf prog, since bpf
> > >    trampoline and bpf prog are allocated via vmalloc, there is chance the
> > >    distance exceeds the max branch range.
> > > - Collect ACK/Review-by, not sure if the ACK and Review-bys for bpf_arch_text_poke()
> > >    should be kept, since the changes to it is not trivial

+1 I need to give it another pass.

> > > - Update some commit messages and comments
> >
> > Given you've been taking a look and had objections in v5, would be great if you
> > can find some cycles for this v6.
>
> Mark's out at the moment, so I wouldn't hold this series up pending his ack.
> However, I agree that it would be good if _somebody_ from the Arm side can
> give it the once over, so I've added Jean-Philippe to cc in case he has time

Makes sense,  Jean-Philippe had worked on BPF trampolines for ARM.

> for a quick review. KP said he would also have a look, as he is interested

Thank you so much Will, I will give this another pass before the end
of the week.

> in this series landing.
>
> Failing that, I'll try to look this week, but I'm off next week and I don't
> want this to miss the merge window on my account.

Thanks for being considerate. Much appreciated.

- KP

>
> Cheers,
>
> Will