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

[Yonghong Song <yhs@fb.com>]

On 7/26/21 9:12 AM, 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,

As Jiri has pointed out, BPF_LINK_TYPE_PERF_EVENT = 7.

>   
>   	MAX_BPF_LINK_TYPE,
>   };
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 9a2068e39d23..80c03bedd6e6 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2906,6 +2906,79 @@ static const struct bpf_link_ops bpf_raw_tp_link_lops = {
>   	.fill_link_info = bpf_raw_tp_link_fill_link_info,
>   };
>   
> +#ifdef CONFIG_PERF_EVENTS
> +struct bpf_perf_link {
> +	struct bpf_link link;
> +	struct file *perf_file;
> +};
> +
> +static void bpf_perf_link_release(struct bpf_link *link)
> +{
> +	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
> +	struct perf_event *event = perf_link->perf_file->private_data;
> +
> +	perf_event_free_bpf_prog(event);
> +	fput(perf_link->perf_file);
> +}
> +
> +static void bpf_perf_link_dealloc(struct bpf_link *link)
> +{
> +	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
> +
> +	kfree(perf_link);
> +}
> +
> +static const struct bpf_link_ops bpf_perf_link_lops = {
> +	.release = bpf_perf_link_release,
> +	.dealloc = bpf_perf_link_dealloc,
> +};
> +
> +static int bpf_perf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> +{
> +	struct bpf_link_primer link_primer;
> +	struct bpf_perf_link *link;
> +	struct perf_event *event;
> +	struct file *perf_file;
> +	int err;
> +
> +	if (attr->link_create.flags)
> +		return -EINVAL;
> +
> +	perf_file = perf_event_get(attr->link_create.target_fd);
> +	if (IS_ERR(perf_file))
> +		return PTR_ERR(perf_file);
> +
> +	link = kzalloc(sizeof(*link), GFP_USER);

add __GFP_NOWARN flag?

> +	if (!link) {
> +		err = -ENOMEM;
> +		goto out_put_file;
> +	}
> +	bpf_link_init(&link->link, BPF_LINK_TYPE_PERF_EVENT, &bpf_perf_link_lops, prog);
> +	link->perf_file = perf_file;
> +
> +	err = bpf_link_prime(&link->link, &link_primer);
> +	if (err) {
> +		kfree(link);
> +		goto out_put_file;
> +	}
> +
> +	event = perf_file->private_data;
> +	err = perf_event_set_bpf_prog(event, prog);
> +	if (err) {
> +		bpf_link_cleanup(&link_primer);

Do you need kfree(link) here?

> +		goto out_put_file;
> +	}
> +	/* perf_event_set_bpf_prog() doesn't take its own refcnt on prog */
> +	bpf_prog_inc(prog);
> +
> +	return bpf_link_settle(&link_primer);
> +
> +out_put_file:
> +	fput(perf_file);
> +	return err;
> +}
> +#endif /* CONFIG_PERF_EVENTS */
> +
>   #define BPF_RAW_TRACEPOINT_OPEN_LAST_FIELD raw_tracepoint.prog_fd
>   
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