netdev - Re: [PATCH v4 bpf-next 1/3] bpf: enable BPF_PROG_TEST_RUN for raw

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Date:   Thu, 24 Sep 2020 20:49:10 +0000
From:   Song Liu <songliubraving@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "Kernel Team" <Kernel-team@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v4 bpf-next 1/3] bpf: enable BPF_PROG_TEST_RUN for
 raw_tracepoint



> On Sep 24, 2020, at 12:56 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> 
> On Wed, Sep 23, 2020 at 6:46 PM Song Liu <songliubraving@...com> wrote:
>> 
>> Add .test_run for raw_tracepoint. Also, introduce a new feature that runs
>> the target program on a specific CPU. This is achieved by a new flag in
>> bpf_attr.test, BPF_F_TEST_RUN_ON_CPU. When this flag is set, the program
>> is triggered on cpu with id bpf_attr.test.cpu. This feature is needed for
>> BPF programs that handle perf_event and other percpu resources, as the
>> program can access these resource locally.
>> 
>> Acked-by: John Fastabend <john.fastabend@...il.com>
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
>> include/linux/bpf.h            |  3 ++
>> include/uapi/linux/bpf.h       |  7 +++
>> kernel/bpf/syscall.c           |  2 +-
>> kernel/trace/bpf_trace.c       |  1 +
>> net/bpf/test_run.c             | 89 ++++++++++++++++++++++++++++++++++
>> tools/include/uapi/linux/bpf.h |  7 +++
>> 6 files changed, 108 insertions(+), 1 deletion(-)
>> 
> 
> [...]
> 
>> +int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
>> +                            const union bpf_attr *kattr,
>> +                            union bpf_attr __user *uattr)
>> +{
>> +       void __user *ctx_in = u64_to_user_ptr(kattr->test.ctx_in);
>> +       __u32 ctx_size_in = kattr->test.ctx_size_in;
>> +       struct bpf_raw_tp_test_run_info info;
>> +       int cpu, err = 0;
>> +
>> +       /* doesn't support data_in/out, ctx_out, duration, or repeat */
>> +       if (kattr->test.data_in || kattr->test.data_out ||
>> +           kattr->test.ctx_out || kattr->test.duration ||
>> +           kattr->test.repeat)
> 
> duration and repeat sound generally useful (benchmarking raw_tp
> programs), so it's a pity you haven't implemented them. But it can be
> added later, so not a deal breaker.
> 
>> +               return -EINVAL;
>> +
>> +       if (ctx_size_in < prog->aux->max_ctx_offset)
>> +               return -EINVAL;
>> +
>> +       if (ctx_size_in) {
>> +               info.ctx = kzalloc(ctx_size_in, GFP_USER);
>> +               if (!info.ctx)
>> +                       return -ENOMEM;
>> +               if (copy_from_user(info.ctx, ctx_in, ctx_size_in)) {
>> +                       err = -EFAULT;
>> +                       goto out;
>> +               }
>> +       } else {
>> +               info.ctx = NULL;
>> +       }
>> +
>> +       info.prog = prog;
>> +       cpu = kattr->test.cpu;
>> +
>> +       if ((kattr->test.flags & BPF_F_TEST_RUN_ON_CPU) == 0 ||
>> +           cpu == smp_processor_id()) {
> 
> should we enforce that cpu == 0 if BPF_F_TEST_RUN_ON_CPU is not set?

Added a test. 

> 
> 
>> +               __bpf_prog_test_run_raw_tp(&info);
>> +       } else {
>> +               /* smp_call_function_single() also checks cpu_online()
>> +                * after csd_lock(). However, since cpu_plus is from user
> 
> cpu_plus leftover in a comment

Fixed. 

> 
>> +                * space, let's do an extra quick check to filter out
>> +                * invalid value before smp_call_function_single().
>> +                */
>> +               if (!cpu_online(cpu)) {
> 
> briefly looking at cpu_online() code, it seems like it's not checking
> that cpu is < NR_CPUS. Should we add a selftest that validates that
> passing unreasonable cpu index doesn't generate warning or invalid
> memory access?

Good catch! We need extra "cpu >= nr_cpu_ids".

Thanks,
Song