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From: Peilin Ye <yepeilin@google.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: bpf <bpf@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	bpf@ietf.org, Xu Kuohai <xukuohai@huaweicloud.com>,
	Eduard Zingerman <eddyz87@gmail.com>,
	David Vernet <void@manifault.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>,
	Yonghong Song <yonghong.song@linux.dev>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Puranjay Mohan <puranjay@kernel.org>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Quentin Monnet <qmo@kernel.org>,
	Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
	Ihor Solodrai <ihor.solodrai@linux.dev>,
	Yingchi Long <longyingchi24s@ict.ac.cn>,
	Josh Don <joshdon@google.com>, Barret Rhoden <brho@google.com>,
	Neel Natu <neelnatu@google.com>,
	Benjamin Segall <bsegall@google.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next v2 4/9] bpf: Introduce load-acquire and store-release instructions
Date: Mon, 10 Feb 2025 22:51:11 +0000	[thread overview]
Message-ID: <Z6qC303CzfUMN8nV@google.com> (raw)
In-Reply-To: <CAADnVQLkHA9LGv99k2TZOJEGUU=dw=q6nVurJ=aoh0v6cFS6zQ@mail.gmail.com>

Hi Alexei,

On Sat, Feb 08, 2025 at 07:46:54PM -0800, Alexei Starovoitov wrote:
> > Got it!  In v3, I'll change it back to:
> >
> >   #define BPF_LOAD_ACQ   0x10
> >   #define BPF_STORE_REL  0x20
> 
> why not 1 and 2 ?

I just realized that we can't do 1 and 2 because BPF_ADD | BPF_FETCH
also equals 1.

> All other bits are reserved and the verifier will make sure they're zero

IOW, we can't tell if imm<4-7> is reserved or BPF_ADD (0x00).  What
would you suggest?  Maybe:

  #define BPF_ATOMIC_LD_ST 0x10

  #define BPF_LOAD_ACQ      0x1
  #define BPF_STORE_REL     0x2

?

> , so when/if we need to extend it then it wouldn't matter whether
> lower 4 bits are reserved or other bits.
> Say, we decide to support cmpwait_relaxed as a new insn.
> It can take the value 3 and arm64 JIT will map it to ldxr+wfe+...
> 
> Then with this new load_acq and cmpwait_relaxed we can efficiently
> implement both smp_cond_load_relaxed and smp_cond_load_acquire.

Thanks,
Peilin Ye


  parent reply	other threads:[~2025-02-10 22:51 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-02-07  2:04 [PATCH bpf-next v2 0/9] Introduce load-acquire and store-release BPF instructions Peilin Ye
2025-02-07  2:05 ` [PATCH bpf-next v2 1/9] bpf/verifier: Factor out atomic_ptr_type_ok() Peilin Ye
2025-02-07  2:05 ` [PATCH bpf-next v2 2/9] bpf/verifier: Factor out check_atomic_rmw() Peilin Ye
2025-02-07  2:05 ` [PATCH bpf-next v2 3/9] bpf/verifier: Factor out check_load_mem() and check_store_reg() Peilin Ye
2025-02-10 23:45   ` Eduard Zingerman
2025-02-07  2:05 ` [PATCH bpf-next v2 4/9] bpf: Introduce load-acquire and store-release instructions Peilin Ye
2025-02-07 11:28   ` Ilya Leoshkevich
2025-02-07 21:23     ` Peilin Ye
2025-02-08 21:30   ` Alexei Starovoitov
2025-02-09  2:21     ` Peilin Ye
2025-02-09  3:46       ` Alexei Starovoitov
2025-02-09 23:41         ` Peilin Ye
2025-02-10 22:51         ` Peilin Ye [this message]
2025-02-12 22:14           ` Peilin Ye
2025-02-13  5:55             ` Alexei Starovoitov
2025-02-13 11:41               ` Peilin Ye
2025-02-15  2:34                 ` Peilin Ye
2025-02-15  3:04                   ` Alexei Starovoitov
2025-02-15  6:17                     ` Peilin Ye
2025-02-07  2:06 ` [PATCH bpf-next v2 5/9] arm64: insn: Add BIT(23) to {load,store}_ex's mask Peilin Ye
2025-02-07  2:06 ` [PATCH bpf-next v2 6/9] arm64: insn: Add load-acquire and store-release instructions Peilin Ye
2025-02-07  2:06 ` [PATCH bpf-next v2 7/9] bpf, arm64: Support " Peilin Ye
2025-02-07  2:06 ` [PATCH bpf-next v2 8/9] selftests/bpf: Add selftests for " Peilin Ye
2025-02-07 23:47   ` Peilin Ye
2025-02-08  0:20   ` Peilin Ye
2025-02-08  2:20     ` Peilin Ye
2025-02-11  0:20       ` Eduard Zingerman
2025-02-11  0:08   ` Eduard Zingerman
2025-02-11 19:09     ` Peilin Ye
2025-02-11 20:15       ` Eduard Zingerman
2025-02-11 20:51         ` Peilin Ye
2025-02-20  1:08           ` Peilin Ye
2025-02-20  1:21             ` Eduard Zingerman
2025-02-07  2:06 ` [PATCH bpf-next v2 9/9] bpf, docs: Update instruction-set.rst " Peilin Ye
2025-02-07 21:29 ` [PATCH bpf-next v2 0/9] Introduce load-acquire and store-release BPF instructions Peilin Ye

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