linux-kernel - Re: [PATCH bpf-next v3 4/9] bpf: Introduce load-acquire and store-release instructions

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Message-ID: <CAADnVQKEcof-WBBj_W=GpsP0Tjm8hyxeWc06243ZBR7_Ua0Gfg@mail.gmail.com>
Date: Wed, 26 Feb 2025 18:18:47 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Peilin Ye <yepeilin@...gle.com>
Cc: bpf <bpf@...r.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, bpf@...f.org, 
	Xu Kuohai <xukuohai@...weicloud.com>, Eduard Zingerman <eddyz87@...il.com>, 
	David Vernet <void@...ifault.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Jonathan Corbet <corbet@....net>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Puranjay Mohan <puranjay@...nel.org>, 
	Ilya Leoshkevich <iii@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Quentin Monnet <qmo@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	Ihor Solodrai <ihor.solodrai@...ux.dev>, Yingchi Long <longyingchi24s@....ac.cn>, 
	Josh Don <joshdon@...gle.com>, Barret Rhoden <brho@...gle.com>, Neel Natu <neelnatu@...gle.com>, 
	Benjamin Segall <bsegall@...gle.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 4/9] bpf: Introduce load-acquire and
 store-release instructions

On Wed, Feb 19, 2025 at 5:21 PM Peilin Ye <yepeilin@...gle.com> wrote:
>
>
> In arch/{arm64,s390,x86}/net/bpf_jit_comp.c, have
> bpf_jit_supports_insn(..., /*in_arena=*/true) return false for the new
> instructions, until the corresponding JIT compiler supports them.

...

> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index a43fc5af973d..f0c31c940fb8 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -3771,8 +3771,12 @@ bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)
>         if (!in_arena)
>                 return true;
>         switch (insn->code) {
> +       case BPF_STX | BPF_ATOMIC | BPF_B:
> +       case BPF_STX | BPF_ATOMIC | BPF_H:
>         case BPF_STX | BPF_ATOMIC | BPF_W:
>         case BPF_STX | BPF_ATOMIC | BPF_DW:
> +               if (bpf_atomic_is_load_store(insn))
> +                       return false;
>                 if (insn->imm == (BPF_AND | BPF_FETCH) ||
>                     insn->imm == (BPF_OR | BPF_FETCH) ||
>                     insn->imm == (BPF_XOR | BPF_FETCH))

It's border line ok-ish to delay arena ld_acq/st_rel on x86 for a follow up,
but non-arena on x86 should be done in this patch.
It's trivial to add support on x86-64 and
limiting the selftest to:
.. defined(__TARGET_ARCH_arm64)
is just not right.

Even arena ld_acq/st_rel can be done in this patch too.
It is such a minor addition compared to the rest, so I don't see
a reason not to do it right away.

pw-bot: cr