* [PATCH] bpf: fix reuse of DEVMAP @ 2025-08-11 9:10 Yureka Lilian 2025-08-11 9:39 ` Yureka Lilian 0 siblings, 1 reply; 4+ messages in thread From: Yureka Lilian @ 2025-08-11 9:10 UTC (permalink / raw) To: bpf; +Cc: Yureka Lilian Previously, re-using pinned DEVMAP maps would always fail, because get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set, it BPF_F_RDONLY_PROG being set on a map being created is invalid. Thus, match the BPF_F_RDONLY_PROG flag being set on the new map when checking for compatibility with an existing DEVMAP The same problem is handled in third-party ebpf library: - https://github.com/cilium/ebpf/issues/925 - https://github.com/cilium/ebpf/pull/930 Signed-off-by: Yureka Lilian <yuka@yuka.dev> --- tools/lib/bpf/libbpf.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index fb4d92c5c..a554d7fff 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5081,6 +5081,7 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) { struct bpf_map_info map_info; __u32 map_info_len = sizeof(map_info); + __u32 map_flags_for_check = map->def.map_flags; int err; memset(&map_info, 0, map_info_len); @@ -5093,11 +5094,20 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) return false; } + /* get_map_info on a DEVMAP will always return flags with + * BPF_F_RDONLY_PROG set, but it will never be set on a map + * being created. + * Thus, match the BPF_F_RDONLY_PROG flag being set on the new + * map when checking for compatibility with an existing DEVMAP + */ + if (map->def.type == BPF_MAP_TYPE_DEVMAP || map->def.type == BPF_MAP_TYPE_DEVMAP_HASH) + map_flags_for_check |= BPF_F_RDONLY_PROG; + return (map_info.type == map->def.type && map_info.key_size == map->def.key_size && map_info.value_size == map->def.value_size && map_info.max_entries == map->def.max_entries && - map_info.map_flags == map->def.map_flags && + map_info.map_flags == map_flags_for_check && map_info.map_extra == map->map_extra); } -- 2.50.1 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH] bpf: fix reuse of DEVMAP 2025-08-11 9:10 [PATCH] bpf: fix reuse of DEVMAP Yureka Lilian @ 2025-08-11 9:39 ` Yureka Lilian 2025-08-11 17:29 ` Eduard Zingerman 2025-08-11 19:38 ` Martin KaFai Lau 0 siblings, 2 replies; 4+ messages in thread From: Yureka Lilian @ 2025-08-11 9:39 UTC (permalink / raw) To: Andrii Nakryiko, Eduard Zingerman, Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa Cc: Yureka Lilian, bpf, linux-kernel Previously, re-using pinned DEVMAP maps would always fail, because get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set, it BPF_F_RDONLY_PROG being set on a map being created is invalid. Thus, match the BPF_F_RDONLY_PROG flag being set on the new map when checking for compatibility with an existing DEVMAP The same problem is handled in third-party ebpf library: - https://github.com/cilium/ebpf/issues/925 - https://github.com/cilium/ebpf/pull/930 Signed-off-by: Yureka Lilian <yuka@yuka.dev> --- tools/lib/bpf/libbpf.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index fb4d92c5c..a554d7fff 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5081,6 +5081,7 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) { struct bpf_map_info map_info; __u32 map_info_len = sizeof(map_info); + __u32 map_flags_for_check = map->def.map_flags; int err; memset(&map_info, 0, map_info_len); @@ -5093,11 +5094,20 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) return false; } + /* get_map_info on a DEVMAP will always return flags with + * BPF_F_RDONLY_PROG set, but it will never be set on a map + * being created. + * Thus, match the BPF_F_RDONLY_PROG flag being set on the new + * map when checking for compatibility with an existing DEVMAP + */ + if (map->def.type == BPF_MAP_TYPE_DEVMAP || map->def.type == BPF_MAP_TYPE_DEVMAP_HASH) + map_flags_for_check |= BPF_F_RDONLY_PROG; + return (map_info.type == map->def.type && map_info.key_size == map->def.key_size && map_info.value_size == map->def.value_size && map_info.max_entries == map->def.max_entries && - map_info.map_flags == map->def.map_flags && + map_info.map_flags == map_flags_for_check && map_info.map_extra == map->map_extra); } -- 2.50.1 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] bpf: fix reuse of DEVMAP 2025-08-11 9:39 ` Yureka Lilian @ 2025-08-11 17:29 ` Eduard Zingerman 2025-08-11 19:38 ` Martin KaFai Lau 1 sibling, 0 replies; 4+ messages in thread From: Eduard Zingerman @ 2025-08-11 17:29 UTC (permalink / raw) To: Yureka Lilian, Andrii Nakryiko, Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa Cc: bpf, linux-kernel On Mon, 2025-08-11 at 11:39 +0200, Yureka Lilian wrote: > Previously, re-using pinned DEVMAP maps would always fail, because > get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set, > it BPF_F_RDONLY_PROG being set on a map being created is invalid. > > Thus, match the BPF_F_RDONLY_PROG flag being set on the new map when > checking for compatibility with an existing DEVMAP > > The same problem is handled in third-party ebpf library: > - https://github.com/cilium/ebpf/issues/925 > - https://github.com/cilium/ebpf/pull/930 > > Signed-off-by: Yureka Lilian <yuka@yuka.dev> > --- The change makes sense to me, could you please add a selftest? [...] ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] bpf: fix reuse of DEVMAP 2025-08-11 9:39 ` Yureka Lilian 2025-08-11 17:29 ` Eduard Zingerman @ 2025-08-11 19:38 ` Martin KaFai Lau 1 sibling, 0 replies; 4+ messages in thread From: Martin KaFai Lau @ 2025-08-11 19:38 UTC (permalink / raw) To: Yureka Lilian Cc: Andrii Nakryiko, Eduard Zingerman, Alexei Starovoitov, Daniel Borkmann, Song Liu, Yonghong Song, John Fastabend, KP Singh, Stanislav Fomichev, Hao Luo, Jiri Olsa, Toke Høiland-Jørgensen, bpf, linux-kernel On 8/11/25 2:39 AM, Yureka Lilian wrote: > Previously, re-using pinned DEVMAP maps would always fail, because > get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set, > it BPF_F_RDONLY_PROG being set on a map being created is invalid. > > Thus, match the BPF_F_RDONLY_PROG flag being set on the new map when > checking for compatibility with an existing DEVMAP > > The same problem is handled in third-party ebpf library: > - https://github.com/cilium/ebpf/issues/925 > - https://github.com/cilium/ebpf/pull/930 > > Signed-off-by: Yureka Lilian <yuka@yuka.dev> This should be a fix for this commit? Fixes: 0cdbb4b09a06 ("devmap: Allow map lookups from eBPF") > --- > tools/lib/bpf/libbpf.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index fb4d92c5c..a554d7fff 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -5081,6 +5081,7 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) > { > struct bpf_map_info map_info; > __u32 map_info_len = sizeof(map_info); > + __u32 map_flags_for_check = map->def.map_flags; > int err; > > memset(&map_info, 0, map_info_len); > @@ -5093,11 +5094,20 @@ static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd) > return false; > } > > + /* get_map_info on a DEVMAP will always return flags with > + * BPF_F_RDONLY_PROG set, but it will never be set on a map > + * being created. > + * Thus, match the BPF_F_RDONLY_PROG flag being set on the new > + * map when checking for compatibility with an existing DEVMAP > + */ > + if (map->def.type == BPF_MAP_TYPE_DEVMAP || map->def.type == BPF_MAP_TYPE_DEVMAP_HASH) > + map_flags_for_check |= BPF_F_RDONLY_PROG; Does it break older kernels that do not set the RDONLY_PROG bit implicitly by itself? > + > return (map_info.type == map->def.type && > map_info.key_size == map->def.key_size && > map_info.value_size == map->def.value_size && > map_info.max_entries == map->def.max_entries && > - map_info.map_flags == map->def.map_flags && > + map_info.map_flags == map_flags_for_check && > map_info.map_extra == map->map_extra); > } > ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2025-08-11 19:38 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2025-08-11 9:10 [PATCH] bpf: fix reuse of DEVMAP Yureka Lilian 2025-08-11 9:39 ` Yureka Lilian 2025-08-11 17:29 ` Eduard Zingerman 2025-08-11 19:38 ` Martin KaFai Lau
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