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Date:   Thu, 7 May 2020 22:19:35 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Luke Nelson <lukenels@...washington.edu>, bpf@...r.kernel.org
Cc:     Luke Nelson <luke.r.nels@...il.com>, Xi Wang <xi.wang@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Enrico Weigelt <info@...ux.net>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [RFC PATCH bpf-next 2/3] bpf, arm64: Optimize AND,OR,XOR,JSET
 BPF_K using arm64 logical immediates

On 5/7/20 3:05 AM, Luke Nelson wrote:
> The current code for BPF_{AND,OR,XOR,JSET} BPF_K loads the immediate to
> a temporary register before use.
> 
> This patch changes the code to avoid using a temporary register
> when the BPF immediate is encodable using an arm64 logical immediate
> instruction. If the encoding fails (due to the immediate not being
> encodable), it falls back to using a temporary register.
> 
> Example of generated code for BPF_ALU32_IMM(BPF_AND, R0, 0x80000001):
> 
> without optimization:
> 
>    24: mov  w10, #0x8000ffff
>    28: movk w10, #0x1
>    2c: and  w7, w7, w10
> 
> with optimization:
> 
>    24: and  w7, w7, #0x80000001
> 
> Since the encoding process is quite complex, the JIT reuses existing
> functionality in arch/arm64/kernel/insn.c for encoding logical immediates
> rather than duplicate it in the JIT.
> 
> Co-developed-by: Xi Wang <xi.wang@...il.com>
> Signed-off-by: Xi Wang <xi.wang@...il.com>
> Signed-off-by: Luke Nelson <luke.r.nels@...il.com>

Great find, thanks! Given Will wanted to queue them:

Acked-by: Daniel Borkmann <daniel@...earbox.net>

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