Re: [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr()

From: Hao Luo <haoluo@google.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>, Shuah Khan <shuah@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andriin@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>, Andrey Ignatov <rdna@fb.com>,
	Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr()
Date: Thu, 27 Aug 2020 20:42:34 -0700	[thread overview]
Message-ID: <CA+khW7jYWNT5aVe5vCinw5qwKKoB0w386qz2g+0ndv1LeeoGGg@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzYC0JRQusCxTrmraYQC7SZdkVjdy8DMUNECKwCbXP9-dw@mail.gmail.com>

Thanks for taking a look!

On Fri, Aug 21, 2020 at 8:30 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Wed, Aug 19, 2020 at 3:42 PM Hao Luo <haoluo@google.com> wrote:
> >
> > Test bpf_per_cpu_ptr(). Test two paths in the kernel. If the base
> > pointer points to a struct, the returned reg is of type PTR_TO_BTF_ID.
> > Direct pointer dereference can be applied on the returned variable.
> > If the base pointer isn't a struct, the returned reg is of type
> > PTR_TO_MEM, which also supports direct pointer dereference.
> >
> > Signed-off-by: Hao Luo <haoluo@google.com>
> > ---
>
> Acked-by: Andrii Nakryiko <andriin@fb.com>
>
[...]
> >
> >  __u64 out__runqueues = -1;
> >  __u64 out__bpf_prog_active = -1;
> > +__u32 out__rq_cpu = -1;
> > +unsigned long out__process_counts = -1;
>
> try to not use long for variables, it is 32-bit integer in user-space
> but always 64-bit in BPF. This causes problems when using skeleton on
> 32-bit architecture.
>

Ack. I will use another variable of type 'int' instead.

> >
> > -extern const struct rq runqueues __ksym; /* struct type global var. */
> > +extern const struct rq runqueues __ksym; /* struct type percpu var. */
> >  extern const int bpf_prog_active __ksym; /* int type global var. */
> > +extern const unsigned long process_counts __ksym; /* int type percpu var. */
> >
> >  SEC("raw_tp/sys_enter")
> >  int handler(const void *ctx)
> >  {
> > +       struct rq *rq;
> > +       unsigned long *count;
> > +
> >         out__runqueues = (__u64)&runqueues;
> >         out__bpf_prog_active = (__u64)&bpf_prog_active;
> >
> > +       rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 1);
> > +       if (rq)
> > +               out__rq_cpu = rq->cpu;
>
> this is awesome!
>
> Are there any per-cpu variables that are arrays? Would be nice to test
> those too.
>
>

There are currently per-cpu arrays, but not common. There is a
'pmc_prev_left' in arch/x86, I can add that in this test.

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