On Mon, 12 Feb 2024 at 20:11, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Fri, Feb 9, 2024 at 11:17 PM Kumar Kartikeya Dwivedi
> <memxor@xxxxxxxxx> wrote:
> >
> > On Fri, 9 Feb 2024 at 05:07, Alexei Starovoitov
> > <alexei.starovoitov@xxxxxxxxx> wrote:
> > >
> > > From: Alexei Starovoitov <ast@xxxxxxxxxx>
> > >
> > > mmap() bpf_arena right after creation, since the kernel needs to
> > > remember the address returned from mmap. This is user_vm_start.
> > > LLVM will generate bpf_arena_cast_user() instructions where
> > > necessary and JIT will add upper 32-bit of user_vm_start
> > > to such pointers.
> > >
> > > Fix up bpf_map_mmap_sz() to compute mmap size as
> > > map->value_size * map->max_entries for arrays and
> > > PAGE_SIZE * map->max_entries for arena.
> > >
> > > Don't set BTF at arena creation time, since it doesn't support it.
> > >
> > > Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> > > ---
> > > tools/lib/bpf/libbpf.c | 43 ++++++++++++++++++++++++++++++-----
> > > tools/lib/bpf/libbpf_probes.c | 7 ++++++
> > > 2 files changed, 44 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index 01f407591a92..4880d623098d 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> > > @@ -185,6 +185,7 @@ static const char * const map_type_name[] = {
> > > [BPF_MAP_TYPE_BLOOM_FILTER] = "bloom_filter",
> > > [BPF_MAP_TYPE_USER_RINGBUF] = "user_ringbuf",
> > > [BPF_MAP_TYPE_CGRP_STORAGE] = "cgrp_storage",
> > > + [BPF_MAP_TYPE_ARENA] = "arena",
> > > };
> > >
> > > static const char * const prog_type_name[] = {
> > > @@ -1577,7 +1578,7 @@ static struct bpf_map *bpf_object__add_map(struct bpf_object *obj)
> > > return map;
> > > }
> > >
> > > -static size_t bpf_map_mmap_sz(unsigned int value_sz, unsigned int max_entries)
> > > +static size_t __bpf_map_mmap_sz(unsigned int value_sz, unsigned int max_entries)
> > > {
> > > const long page_sz = sysconf(_SC_PAGE_SIZE);
> > > size_t map_sz;
> > > @@ -1587,6 +1588,20 @@ static size_t bpf_map_mmap_sz(unsigned int value_sz, unsigned int max_entries)
> > > return map_sz;
> > > }
> > >
> > > +static size_t bpf_map_mmap_sz(const struct bpf_map *map)
> > > +{
> > > + const long page_sz = sysconf(_SC_PAGE_SIZE);
> > > +
> > > + switch (map->def.type) {
> > > + case BPF_MAP_TYPE_ARRAY:
> > > + return __bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
> > > + case BPF_MAP_TYPE_ARENA:
> > > + return page_sz * map->def.max_entries;
> > > + default:
> > > + return 0; /* not supported */
> > > + }
> > > +}
> > > +
> > > static int bpf_map_mmap_resize(struct bpf_map *map, size_t old_sz, size_t new_sz)
> > > {
> > > void *mmaped;
> > > @@ -1740,7 +1755,7 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> > > pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %x.\n",
> > > map->name, map->sec_idx, map->sec_offset, def->map_flags);
> > >
> > > - mmap_sz = bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
> > > + mmap_sz = bpf_map_mmap_sz(map);
> > > map->mmaped = mmap(NULL, mmap_sz, PROT_READ | PROT_WRITE,
> > > MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> > > if (map->mmaped == MAP_FAILED) {
> > > @@ -4852,6 +4867,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
> > > case BPF_MAP_TYPE_SOCKHASH:
> > > case BPF_MAP_TYPE_QUEUE:
> > > case BPF_MAP_TYPE_STACK:
> > > + case BPF_MAP_TYPE_ARENA:
> > > create_attr.btf_fd = 0;
> > > create_attr.btf_key_type_id = 0;
> > > create_attr.btf_value_type_id = 0;
> > > @@ -4908,6 +4924,21 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
> > > if (map->fd == map_fd)
> > > return 0;
> > >
> > > + if (def->type == BPF_MAP_TYPE_ARENA) {
> > > + map->mmaped = mmap((void *)map->map_extra, bpf_map_mmap_sz(map),
> > > + PROT_READ | PROT_WRITE,
> > > + map->map_extra ? MAP_SHARED | MAP_FIXED : MAP_SHARED,
> > > + map_fd, 0);
> > > + if (map->mmaped == MAP_FAILED) {
> > > + err = -errno;
> > > + map->mmaped = NULL;
> > > + close(map_fd);
> > > + pr_warn("map '%s': failed to mmap bpf_arena: %d\n",
> > > + bpf_map__name(map), err);
> > > + return err;
> > > + }
> > > + }
> > > +
> >
> > Would it be possible to introduce a public API accessor for getting
> > the value of map->mmaped?
>
> That would be bpf_map__initial_value(), no?
>
Ah, indeed, that would do the trick. Thanks Andrii!
> [...]
