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

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Date:   Fri, 13 May 2022 16:37:04 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Hari Bathini <hbathini@...ux.ibm.com>, bpf@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc:     "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

Daniel Borkmann <daniel@...earbox.net> writes:
> 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?

Yeah I'm happy to take them if they are OK by you.

I do wonder if the BPF jit code should eventually move out of arch/, but
that's a discussion for another day.

> 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.

Yes please, test results make me feel much better about merging things :)

cheers