netdev - Re: [PATCH 0/5] Atomics support for eBPF on powerpc

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Date:   Thu, 12 May 2022 20:40:54 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Hari Bathini <hbathini@...ux.ibm.com>, bpf@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        netdev@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Jordan Niethe <jniethe5@...il.com>
Subject: Re: [PATCH 0/5] Atomics support for eBPF on powerpc

On 5/12/22 9:45 AM, Hari Bathini wrote:
> This patchset adds atomic operations to the eBPF instruction set on
> powerpc. The instructions that are added here can be summarised with
> this list of kernel operations for ppc64:
> 
> * atomic[64]_[fetch_]add
> * atomic[64]_[fetch_]and
> * atomic[64]_[fetch_]or
> * atomic[64]_[fetch_]xor
> * atomic[64]_xchg
> * atomic[64]_cmpxchg
> 
> and this list of kernel operations for ppc32:
> 
> * atomic_[fetch_]add
> * atomic_[fetch_]and
> * atomic_[fetch_]or
> * atomic_[fetch_]xor
> * atomic_xchg
> * atomic_cmpxchg
> 
> The following are left out of scope for this effort:
> 
> * 64 bit operations on ppc32.
> * Explicit memory barriers, 16 and 8 bit operations on both ppc32
>    & ppc64.
> 
> The first patch adds support for bitwsie atomic operations on ppc64.
> The next patch adds fetch variant support for these instructions. The
> third patch adds support for xchg and cmpxchg atomic operations on
> ppc64. Patch #4 adds support for 32-bit atomic bitwise operations on
> ppc32. patch #5 adds support for xchg and cmpxchg atomic operations
> on ppc32.

Thanks for adding these, Hari! I presume they'll get routed via Michael,
right? One thing that may be worth adding to the commit log as well is
the test result from test_bpf.ko given it has an extensive suite around
atomics useful for testing corner cases in JITs.

> Hari Bathini (5):
>    bpf ppc64: add support for BPF_ATOMIC bitwise operations
>    bpf ppc64: add support for atomic fetch operations
>    bpf ppc64: Add instructions for atomic_[cmp]xchg
>    bpf ppc32: add support for BPF_ATOMIC bitwise operations
>    bpf ppc32: Add instructions for atomic_[cmp]xchg
> 
>   arch/powerpc/net/bpf_jit_comp32.c | 62 +++++++++++++++++-----
>   arch/powerpc/net/bpf_jit_comp64.c | 87 +++++++++++++++++++++----------
>   2 files changed, 108 insertions(+), 41 deletions(-)
>