netdev - Re: [PATCH bpf-next 1/3] perf/core: introduce perf_event_mmap_bpf

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Message-ID: <4DBB524C-09B1-46BD-A56E-1E372E87F2E8@fb.com>
Date:   Wed, 19 Sep 2018 23:30:17 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexei Starovoitov <ast@...nel.org>
CC:     "David S . Miller" <davem@...emloft.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 1/3] perf/core: introduce
 perf_event_mmap_bpf_prog



> On Sep 19, 2018, at 3:39 PM, Alexei Starovoitov <ast@...nel.org> wrote:
> 
> introduce perf_event_mmap_bpf_prog() helper to emit RECORD_MMAP events
> into perf ring buffer.
> It's used by bpf load/unload logic to notify user space of addresses
> and names of JITed bpf programs.
> 
> Note that event->mmap.pid == -1 is an existing indicator of kernel event.
> In addition use event->mmap.tid == BPF_FS_MAGIC to indicate bpf related
> RECORD_MMAP event.
> 
> Alternatively it's possible to introduce new 'enum perf_event_type' command
> specificially for bpf prog load/unload, but existing RECORD_MMAP
> is very close, so the choice made by this patch is to extend it.
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Acked-by: Song Liu <songliubraving@...com>

I guess we should also use this for kernel modules load/unload? 


> ---
> include/linux/perf_event.h |  1 +
> kernel/events/core.c       | 44 +++++++++++++++++++++++++++++++++-----
> 2 files changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 53c500f0ca79..0e79af83138f 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1113,6 +1113,7 @@ static inline void perf_event_task_sched_out(struct task_struct *prev,
> }
> 
> extern void perf_event_mmap(struct vm_area_struct *vma);
> +void perf_event_mmap_bpf_prog(u64 start, u64 len, char *name, int size);
> extern struct perf_guest_info_callbacks *perf_guest_cbs;
> extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
> extern int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2a62b96600ad..c48244ddf993 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7152,7 +7152,7 @@ static int perf_event_mmap_match(struct perf_event *event,
> {
> 	struct perf_mmap_event *mmap_event = data;
> 	struct vm_area_struct *vma = mmap_event->vma;
> -	int executable = vma->vm_flags & VM_EXEC;
> +	int executable = !vma || vma->vm_flags & VM_EXEC;
> 
> 	return (!executable && event->attr.mmap_data) ||
> 	       (executable && (event->attr.mmap || event->attr.mmap2));
> @@ -7165,12 +7165,13 @@ static void perf_event_mmap_output(struct perf_event *event,
> 	struct perf_output_handle handle;
> 	struct perf_sample_data sample;
> 	int size = mmap_event->event_id.header.size;
> +	bool bpf_event = !mmap_event->vma;
> 	int ret;
> 
> 	if (!perf_event_mmap_match(event, data))
> 		return;
> 
> -	if (event->attr.mmap2) {
> +	if (event->attr.mmap2 && !bpf_event) {
> 		mmap_event->event_id.header.type = PERF_RECORD_MMAP2;
> 		mmap_event->event_id.header.size += sizeof(mmap_event->maj);
> 		mmap_event->event_id.header.size += sizeof(mmap_event->min);
> @@ -7186,12 +7187,14 @@ static void perf_event_mmap_output(struct perf_event *event,
> 	if (ret)
> 		goto out;
> 
> -	mmap_event->event_id.pid = perf_event_pid(event, current);
> -	mmap_event->event_id.tid = perf_event_tid(event, current);
> +	if (!bpf_event) {
> +		mmap_event->event_id.pid = perf_event_pid(event, current);
> +		mmap_event->event_id.tid = perf_event_tid(event, current);
> +	}
> 
> 	perf_output_put(&handle, mmap_event->event_id);
> 
> -	if (event->attr.mmap2) {
> +	if (event->attr.mmap2 && !bpf_event) {
> 		perf_output_put(&handle, mmap_event->maj);
> 		perf_output_put(&handle, mmap_event->min);
> 		perf_output_put(&handle, mmap_event->ino);
> @@ -7448,6 +7451,37 @@ void perf_event_mmap(struct vm_area_struct *vma)
> 	perf_event_mmap_event(&mmap_event);
> }
> 
> +void perf_event_mmap_bpf_prog(u64 start, u64 len, char *name, int size)
> +{
> +	struct perf_mmap_event mmap_event;
> +
> +	if (!atomic_read(&nr_mmap_events))
> +		return;
> +
> +	if (!IS_ALIGNED(size, sizeof(u64))) {
> +		WARN_ONCE(1, "size is not aligned\n");
> +		return;
> +	}
> +
> +	mmap_event = (struct perf_mmap_event){
> +		.file_name = name,
> +		.file_size = size,
> +		.event_id  = {
> +			.header = {
> +				.type = PERF_RECORD_MMAP,
> +				.misc = PERF_RECORD_MISC_KERNEL,
> +				.size = sizeof(mmap_event.event_id) + size,
> +			},
> +			.pid = -1, /* indicates kernel */
> +			.tid = BPF_FS_MAGIC, /* bpf mmap event */
> +			.start  = start,
> +			.len    = len,
> +			.pgoff  = start,
> +		},
> +	};
> +	perf_iterate_sb(perf_event_mmap_output, &mmap_event, NULL);
> +}
> +
> void perf_event_aux_event(struct perf_event *event, unsigned long head,
> 			  unsigned long size, u64 flags)
> {
> -- 
> 2.17.1
>