linux-kernel - Re: [PATCH bpf-next v1 7/8] selftests/bpf: Add selftests for load-acquire and store-release instructions

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Message-ID: <Z5rBtxNnGHjJaZEt@google.com>
Date: Thu, 30 Jan 2025 00:03:03 +0000
From: Peilin Ye <yepeilin@...gle.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, bpf@...f.org,
	Xu Kuohai <xukuohai@...weicloud.com>,
	David Vernet <void@...ifault.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Puranjay Mohan <puranjay@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Quentin Monnet <qmo@...nel.org>,
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
	Josh Don <joshdon@...gle.com>, Barret Rhoden <brho@...gle.com>,
	Neel Natu <neelnatu@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>, linux-kernel@...r.kernel.org,
	Ihor Solodrai <ihor.solodrai@...ux.dev>
Subject: Re: [PATCH bpf-next v1 7/8] selftests/bpf: Add selftests for
 load-acquire and store-release instructions

On Tue, Jan 28, 2025 at 05:06:03PM -0800, Eduard Zingerman wrote:
> On Sat, 2025-01-25 at 02:19 +0000, Peilin Ye wrote:
> > All new tests depend on the pre-defined __BPF_FEATURE_LOAD_ACQ_STORE_REL
> > feature macro, which implies -mcpu>=v4.
> 
> This restriction would mean that tests are skipped on BPF CI, as it
> currently runs using llvm 17 and 18. Instead, I suggest using some
> macro hiding an inline assembly as below:
> 
> 	asm volatile (".8byte %[insn];"
> 	              :
> 	              : [insn]"i"(*(long *)&(BPF_RAW_INSN(...)))
> 	              : /* correct clobbers here */);
> 
> See the usage of the __imm_insn() macro in the test suite.

I see, I'll do this in v2.

> Also, "BPF_ATOMIC loads from R%d %s is not allowed\n" and
>       "BPF_ATOMIC stores into R%d %s is not allowed\n"
> situations are not tested.

Thanks!

> > --- a/tools/testing/selftests/bpf/prog_tests/atomics.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/atomics.c
> > @@ -162,6 +162,56 @@ static void test_xchg(struct atomics_lskel *skel)
> >  	ASSERT_EQ(skel->bss->xchg32_result, 1, "xchg32_result");
> >  }
> 
> Nit: Given the tests in verifier_load_acquire.c and verifier_store_release.c
>      that use __retval annotation, are these tests really necessary?
>      (assuming that verifier_store_release.c tests are modified to read
>       stored location into r0 before exit).
> 
> > +static void test_load_acquire(struct atomics_lskel *skel)

Ah, right.  I'll drop them and modify verifier_store_release.c
accordingly.

> > --- a/tools/testing/selftests/bpf/progs/arena_atomics.c
> > +++ b/tools/testing/selftests/bpf/progs/arena_atomics.c
> [...]
> 
> > +SEC("raw_tp/sys_enter")
> > +int load_acquire(const void *ctx)
> > +{
> > +	if (pid != (bpf_get_current_pid_tgid() >> 32))
> > +		return 0;
> 
> Nit: This check is not needed, since bpf_prog_test_run_opts() is used
>      to run the tests.

Got it!

Thanks,
Peilin Ye