Re: [PATCH bpf-next v2 6/6] bpf/selftests: Test for bpf_per_cpu_ptr() and bpf_this_cpu_ptr()

On Thu, Sep 3, 2020 at 3:35 PM Hao Luo haoluo@google.com wrote:

Test bpf_per_cpu_ptr() and bpf_this_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.

Acked-by: Andrii Nakryiko andriin@fb.com Signed-off-by: Hao Luo haoluo@google.com

---

.../selftests/bpf/prog_tests/ksyms_btf.c | 10 +++++++ .../selftests/bpf/progs/test_ksyms_btf.c | 26 +++++++++++++++++++ 2 files changed, 36 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c index 7b6846342449..22cc642dbc0e 100644 --- a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c +++ b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c @@ -58,6 +58,16 @@ void test_ksyms_btf(void) CHECK(data->out__bpf_prog_active != bpf_prog_active_addr, "bpf_prog_active", "got %llu, exp %llu\n", data->out__bpf_prog_active, bpf_prog_active_addr);

•   CHECK(data->out__rq_cpu == -1, "rq_cpu",
  

•         "got %u, exp != -1\n", data->out__rq_cpu);
  

•   CHECK(data->out__percpu_bpf_prog_active == -1, "percpu_bpf_prog_active",
  

•         "got %d, exp != -1\n", data->out__percpu_bpf_prog_active);
  

•   CHECK(data->out__this_rq_cpu == -1, "this_rq_cpu",
  

•         "got %u, exp != -1\n", data->out__this_rq_cpu);
  

•   CHECK(data->out__this_bpf_prog_active == -1, "this_bpf_prog_active",
  

•         "got %d, exp != -1\n", data->out__this_bpf_prog_active);
  

see below for few suggestions to make these test more specific

out__this_bpf_prog_active it should always be > 0, no?

cleanup: test_ksyms_btf__destroy(skel); } diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_btf.c b/tools/testing/selftests/bpf/progs/test_ksyms_btf.c index e04e31117f84..02d564349892 100644 --- a/tools/testing/selftests/bpf/progs/test_ksyms_btf.c +++ b/tools/testing/selftests/bpf/progs/test_ksyms_btf.c @@ -8,15 +8,41 @@ __u64 out__runqueues = -1; __u64 out__bpf_prog_active = -1;

+__u32 out__rq_cpu = -1; /* percpu struct fields */ +int out__percpu_bpf_prog_active = -1; /* percpu int */

+__u32 out__this_rq_cpu = -1; +int out__this_bpf_prog_active = -1;

extern const struct rq runqueues __ksym; /* struct type global var. */ extern const int bpf_prog_active __ksym; /* int type global var. */

SEC("raw_tp/sys_enter") int handler(const void *ctx) {

•   struct rq *rq;
  

•   int *active;
  

•   __u32 cpu;
  

•   out__runqueues = (__u64)&runqueues;
    out__bpf_prog_active = (__u64)&bpf_prog_active;
  
  

•   cpu = bpf_get_smp_processor_id();
  

•   /* test bpf_per_cpu_ptr() */
  

•   rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, cpu);
  

•   if (rq)
  

•           out__rq_cpu = rq->cpu;
  

•   active = (int *)bpf_per_cpu_ptr(&bpf_prog_active, cpu);
  

•   if (active)
  

•           out__percpu_bpf_prog_active = *active;
  

this is equivalent to using bpf_this_cpu_ptr(), so:

1. you can compare value with out__this_xxx in user-space

2. it's interesting to also test that you can read value from some other CPU. Can you add another variable and get value from CPU #0 always? E.g., for out__cpu_0_rq_cpu it should always be zero, right?

•   /* test bpf_this_cpu_ptr */
  

•   rq = (struct rq *)bpf_this_cpu_ptr(&runqueues);
  

•   out__this_rq_cpu = rq->cpu;
  

•   active = (int *)bpf_this_cpu_ptr(&bpf_prog_active);
  

•   out__this_bpf_prog_active = *active;
  

•   return 0;
  

}

-- 2.28.0.526.ge36021eeef-goog