Re: [PATCH v2 bpf-next 04/14] bpf: implement minimal BPF perf link

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Jul 26, 2021 at 09:12:01AM -0700, Andrii Nakryiko wrote:
> Introduce a new type of BPF link - BPF perf link. This brings perf_event-based
> BPF program attachments (perf_event, tracepoints, kprobes, and uprobes) into
> the common BPF link infrastructure, allowing to list all active perf_event
> based attachments, auto-detaching BPF program from perf_event when link's FD
> is closed, get generic BPF link fdinfo/get_info functionality.
> 
> BPF_LINK_CREATE command expects perf_event's FD as target_fd. No extra flags
> are currently supported.
> 
> Force-detaching and atomic BPF program updates are not yet implemented, but
> with perf_event-based BPF links we now have common framework for this without
> the need to extend ioctl()-based perf_event interface.
> 
> One interesting consideration is a new value for bpf_attach_type, which
> BPF_LINK_CREATE command expects. Generally, it's either 1-to-1 mapping from
> bpf_attach_type to bpf_prog_type, or many-to-1 mapping from a subset of
> bpf_attach_types to one bpf_prog_type (e.g., see BPF_PROG_TYPE_SK_SKB or
> BPF_PROG_TYPE_CGROUP_SOCK). In this case, though, we have three different
> program types (KPROBE, TRACEPOINT, PERF_EVENT) using the same perf_event-based
> mechanism, so it's many bpf_prog_types to one bpf_attach_type. I chose to
> define a single BPF_PERF_EVENT attach type for all of them and adjust
> link_create()'s logic for checking correspondence between attach type and
> program type.
> 
> The alternative would be to define three new attach types (e.g., BPF_KPROBE,
> BPF_TRACEPOINT, and BPF_PERF_EVENT), but that seemed like unnecessary overkill
> and BPF_KPROBE will cause naming conflicts with BPF_KPROBE() macro, defined by
> libbpf. I chose to not do this to avoid unnecessary proliferation of
> bpf_attach_type enum values and not have to deal with naming conflicts.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  include/linux/bpf_types.h      |   3 +
>  include/linux/trace_events.h   |   3 +
>  include/uapi/linux/bpf.h       |   2 +
>  kernel/bpf/syscall.c           | 105 ++++++++++++++++++++++++++++++---
>  kernel/events/core.c           |  10 ++--
>  tools/include/uapi/linux/bpf.h |   2 +
>  6 files changed, 112 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index a9db1eae6796..0a1ada7f174d 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -135,3 +135,6 @@ BPF_LINK_TYPE(BPF_LINK_TYPE_ITER, iter)
>  #ifdef CONFIG_NET
>  BPF_LINK_TYPE(BPF_LINK_TYPE_NETNS, netns)
>  #endif
> +#ifdef CONFIG_PERF_EVENTS
> +BPF_LINK_TYPE(BPF_LINK_TYPE_PERF_EVENT, perf)
> +#endif
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index ad413b382a3c..8ac92560d3a3 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -803,6 +803,9 @@ extern void ftrace_profile_free_filter(struct perf_event *event);
>  void perf_trace_buf_update(void *record, u16 type);
>  void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp);
>  
> +int perf_event_set_bpf_prog(struct perf_event *event, struct bpf_prog *prog);
> +void perf_event_free_bpf_prog(struct perf_event *event);
> +
>  void bpf_trace_run1(struct bpf_prog *prog, u64 arg1);
>  void bpf_trace_run2(struct bpf_prog *prog, u64 arg1, u64 arg2);
>  void bpf_trace_run3(struct bpf_prog *prog, u64 arg1, u64 arg2,
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 2db6925e04f4..00b1267ab4f0 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -993,6 +993,7 @@ enum bpf_attach_type {
>  	BPF_SK_SKB_VERDICT,
>  	BPF_SK_REUSEPORT_SELECT,
>  	BPF_SK_REUSEPORT_SELECT_OR_MIGRATE,
> +	BPF_PERF_EVENT,
>  	__MAX_BPF_ATTACH_TYPE
>  };
>  
> @@ -1006,6 +1007,7 @@ enum bpf_link_type {
>  	BPF_LINK_TYPE_ITER = 4,
>  	BPF_LINK_TYPE_NETNS = 5,
>  	BPF_LINK_TYPE_XDP = 6,
> +	BPF_LINK_TYPE_PERF_EVENT = 6,

hi, should be 7

jirka