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

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Date:   Tue, 5 Jul 2022 17:00:46 +0100
From:   Will Deacon <will@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>,
        jean-philippe.brucker@....com
Cc:     Xu Kuohai <xukuohai@...wei.com>, bpf@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        James Morse <james.morse@....com>,
        Hou Tao <houtao1@...wei.com>,
        Jason Wang <wangborong@...rlc.com>
Subject: Re: [PATCH bpf-next v6 0/4] bpf trampoline for arm64

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

Cheers,

Will