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Date: Tue, 29 Sep 2020 16:02:10 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Song Liu <songliubraving@...com>, netdev@...r.kernel.org, bpf@...r.kernel.org Cc: kernel-team@...com, ast@...nel.org, john.fastabend@...il.com, kpsingh@...omium.org Subject: Re: [PATCH bpf-next 1/2] bpf: introduce BPF_F_SHARE_PE for perf event array On 9/29/20 10:47 AM, Song Liu wrote: > Currently, perf event in perf event array is removed from the array when > the map fd used to add the event is closed. This behavior makes it > difficult to the share perf events with perf event array. > > Introduce perf event map that keeps the perf event open with a new flag > BPF_F_SHARE_PE. With this flag set, perf events in the array are not > removed when the original map fd is closed. Instead, the perf event will > stay in the map until 1) it is explicitly removed from the array; or 2) > the array is freed. > > Signed-off-by: Song Liu <songliubraving@...com> > --- > include/uapi/linux/bpf.h | 3 +++ > kernel/bpf/arraymap.c | 31 +++++++++++++++++++++++++++++-- > tools/include/uapi/linux/bpf.h | 3 +++ > 3 files changed, 35 insertions(+), 2 deletions(-) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index 82522f05c0213..74f7a09e9d1e3 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -414,6 +414,9 @@ enum { > > /* Enable memory-mapping BPF map */ > BPF_F_MMAPABLE = (1U << 10), > + > +/* Share perf_event among processes */ > + BPF_F_SHARE_PE = (1U << 11), nit but given UAPI: maybe name into something more self-descriptive like BPF_F_SHAREABLE_EVENT ? > }; > > /* Flags for BPF_PROG_QUERY. */ > diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c > index e5fd31268ae02..4938ff183d846 100644 > --- a/kernel/bpf/arraymap.c > +++ b/kernel/bpf/arraymap.c > @@ -15,7 +15,7 @@ > #include "map_in_map.h" > > #define ARRAY_CREATE_FLAG_MASK \ > - (BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK) > + (BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK | BPF_F_SHARE_PE) > > static void bpf_array_free_percpu(struct bpf_array *array) > { > @@ -64,6 +64,10 @@ int array_map_alloc_check(union bpf_attr *attr) > attr->map_flags & BPF_F_MMAPABLE) > return -EINVAL; > > + if (attr->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY && > + attr->map_flags & BPF_F_SHARE_PE) > + return -EINVAL; > + > if (attr->value_size > KMALLOC_MAX_SIZE) > /* if value_size is bigger, the user space won't be able to > * access the elements. > @@ -778,6 +782,26 @@ static int fd_array_map_delete_elem(struct bpf_map *map, void *key) > } > } > > +static void perf_event_fd_array_map_free(struct bpf_map *map) > +{ > + struct bpf_event_entry *ee; > + struct bpf_array *array; > + int i; > + > + if ((map->map_flags & BPF_F_SHARE_PE) == 0) { > + fd_array_map_free(map); > + return; > + } > + > + array = container_of(map, struct bpf_array, map); > + for (i = 0; i < array->map.max_entries; i++) { > + ee = READ_ONCE(array->ptrs[i]); > + if (ee) > + fd_array_map_delete_elem(map, &i); > + } > + bpf_map_area_free(array); Why not simplify into: if (map->map_flags & BPF_F_SHAREABLE_EVENT) bpf_fd_array_map_clear(map); fd_array_map_free(map); > +} > + > static void *prog_fd_array_get_ptr(struct bpf_map *map, > struct file *map_file, int fd) > { > @@ -1134,6 +1158,9 @@ static void perf_event_fd_array_release(struct bpf_map *map, > struct bpf_event_entry *ee; > int i; > > + if (map->map_flags & BPF_F_SHARE_PE) > + return; > + > rcu_read_lock(); > for (i = 0; i < array->map.max_entries; i++) { > ee = READ_ONCE(array->ptrs[i]); > @@ -1148,7 +1175,7 @@ const struct bpf_map_ops perf_event_array_map_ops = { > .map_meta_equal = bpf_map_meta_equal, > .map_alloc_check = fd_array_map_alloc_check, > .map_alloc = array_map_alloc, > - .map_free = fd_array_map_free, > + .map_free = perf_event_fd_array_map_free, > .map_get_next_key = array_map_get_next_key, > .map_lookup_elem = fd_array_map_lookup_elem, > .map_delete_elem = fd_array_map_delete_elem, > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h > index 82522f05c0213..74f7a09e9d1e3 100644 > --- a/tools/include/uapi/linux/bpf.h > +++ b/tools/include/uapi/linux/bpf.h > @@ -414,6 +414,9 @@ enum { > > /* Enable memory-mapping BPF map */ > BPF_F_MMAPABLE = (1U << 10), > + > +/* Share perf_event among processes */ > + BPF_F_SHARE_PE = (1U << 11), > }; > > /* Flags for BPF_PROG_QUERY. */ >
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