linux-kernel - Re: [PATCH bpf-next v5 09/11] bpf: Add bitwise atomic instructions

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Message-ID: <b1a991a8-4254-285c-d72e-029de284f50c@fb.com>
Date:   Tue, 15 Dec 2020 22:53:51 -0800
From:   Yonghong Song <yhs@...com>
To:     Brendan Jackman <jackmanb@...gle.com>, <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 09/11] bpf: Add bitwise atomic instructions



On 12/15/20 4:18 AM, Brendan Jackman wrote:
> This adds instructions for
> 
> atomic[64]_[fetch_]and
> atomic[64]_[fetch_]or
> atomic[64]_[fetch_]xor
> 
> All these operations are isomorphic enough to implement with the same
> verifier, interpreter, and x86 JIT code, hence being a single commit.
> 
> The main interesting thing here is that x86 doesn't directly support
> the fetch_ version these operations, so we need to generate a CMPXCHG
> loop in the JIT. This requires the use of two temporary registers,
> IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.
> 
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>

Acked-by: Yonghong Song <yhs@...com>