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Subject: Re: [PATCH bpf-next 2/2] arm64, bpf: support more atomic operations
To:     Hou Tao <houtao1@huawei.com>, Alexei Starovoitov <ast@kernel.org>
Cc:     Martin KaFai Lau <kafai@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Song Liu <songliubraving@fb.com>,
        "David S . Miller" <davem@davemloft.net>,
        John Fastabend <john.fastabend@gmail.com>,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        Zi Shen Lim <zlim.lnx@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Julien Thierry <jthierry@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        linux-arm-kernel@lists.infradead.org
References: <20220121135632.136976-1-houtao1@huawei.com>
 <20220121135632.136976-3-houtao1@huawei.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <2dca37b0-6eed-38d5-3491-1febf80bd50d@iogearbox.net>
Date:   Fri, 28 Jan 2022 11:06:05 +0100
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On 1/21/22 2:56 PM, Hou Tao wrote:
> Atomics for eBPF patch series adds support for atomic[64]_fetch_add,
> atomic[64]_[fetch_]{and,or,xor} and atomic[64]_{xchg|cmpxchg}, but
> it only add support for x86-64, so support these atomic operations
> for arm64 as well.
> 
> Basically the implementation procedure is almost mechanical translation
> of code snippets in atomic_ll_sc.h & atomic_lse.h & cmpxchg.h located
> under arch/arm64/include/asm. An extra temporary register is needed
> for (BPF_ADD | BPF_FETCH) to save the value of src register, instead of
> adding TMP_REG_4 just use BPF_REG_AX instead.
> 
> For cpus_have_cap(ARM64_HAS_LSE_ATOMICS) case and no-LSE-ATOMICS case,
> both ./test_verifier and "./test_progs -t atomic" are exercised and
> passed correspondingly.

Please also make sure that lib/test_bpf.ko passes given it has the most
extensive tests around atomics.

Thanks,
Daniel