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  1. 07 Mar, 2023 4 commits
    • Yafang Shao's avatar
      bpf: lpm_trie memory usage · 41d5941e
      Yafang Shao authored 
      trie_mem_usage() is introduced to calculate the lpm_trie memory usage.
Some small memory allocations are ignored. The inner node is also
ignored.

The result as follows,

- before
10: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 65536  memlock 1048576B

- after
10: lpm_trie  flags 0x1
        key 8B  value 8B  max_entries 65536  memlock 2291536B
Signed-off-by: default avatarYafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-3-laoar.shao@gmail.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      41d5941e
    • Yafang Shao's avatar
      bpf: add new map ops ->map_mem_usage · 90a5527d
      Yafang Shao authored 
      Add a new map ops ->map_mem_usage to print the memory usage of a
bpf map.

This is a preparation for the followup change.
Signed-off-by: default avatarYafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-2-laoar.shao@gmail.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      90a5527d
    • Nathan Chancellor's avatar
      bpf: Increase size of BTF_ID_LIST without CONFIG_DEBUG_INFO_BTF again · 2d5bcdcd
      Nathan Chancellor authored 
      After commit 66e3a13e ("bpf: Add bpf_dynptr_slice and bpf_dynptr_slice_rdwr"),
clang builds without CONFIG_DEBUG_INFO_BTF warn:

  kernel/bpf/verifier.c:10298:24: warning: array index 16 is past the end of the array (that has type 'u32[16]' (aka 'unsigned int[16]')) [-Warray-bounds]
                                     meta.func_id == special_kfunc_list[KF_bpf_dynptr_slice_rdwr]) {
                                                     ^                  ~~~~~~~~~~~~~~~~~~~~~~~~
  kernel/bpf/verifier.c:9150:1: note: array 'special_kfunc_list' declared here
  BTF_ID_LIST(special_kfunc_list)
  ^
  include/linux/btf_ids.h:207:27: note: expanded from macro 'BTF_ID_LIST'
  #define BTF_ID_LIST(name) static u32 __maybe_unused name[16];
                            ^
  1 warning generated.

A warning of this nature was previously addressed by
commit beb3d47d ("bpf: Fix a BTF_ID_LIST bug with CONFIG_DEBUG_INFO_BTF not set")
but there have been new kfuncs added since then.

Quadruple the size of the CONFIG_DEBUG_INFO_BTF=n definition so that
this problem is unlikely to show up for some time.

Link: https://github.com/ClangBuiltLinux/linux/issues/1810Signed-off-by: default avatarNathan Chancellor <nathan@kernel.org>
Reviewed-by: default avatarTom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20230307-bpf-kfuncs-warray-bounds-v1-1-00ad3191f3a6@kernel.orgSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      2d5bcdcd
    • Jakub Kicinski's avatar
      Merge tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next · 36e5e391
      Jakub Kicinski authored 
      Daniel Borkmann says:

====================
pull-request: bpf-next 2023-03-06

We've added 85 non-merge commits during the last 13 day(s) which contain
a total of 131 files changed, 7102 insertions(+), 1792 deletions(-).

The main changes are:

1) Add skb and XDP typed dynptrs which allow BPF programs for more
   ergonomic and less brittle iteration through data and variable-sized
   accesses, from Joanne Koong.

2) Bigger batch of BPF verifier improvements to prepare for upcoming BPF
   open-coded iterators allowing for less restrictive looping capabilities,
   from Andrii Nakryiko.

3) Rework RCU enforcement in the verifier, add kptr_rcu and enforce BPF
   programs to NULL-check before passing such pointers into kfunc,
   from Alexei Starovoitov.

4) Add support for kptrs in percpu hashmaps, percpu LRU hashmaps and in
   local storage maps, from Kumar Kartikeya Dwivedi.

5) Add BPF verifier support for ST instructions in convert_ctx_access()
   which will help new -mcpu=v4 clang flag to start emitting them,
   from Eduard Zingerman.

6) Make uprobe attachment Android APK aware by supporting attachment
   to functions inside ELF objects contained in APKs via function names,
   from Daniel Müller.

7) Add a new flag BPF_F_TIMER_ABS flag for bpf_timer_start() helper
   to start the timer with absolute expiration value instead of relative
   one, from Tero Kristo.

8) Add a new kfunc bpf_cgroup_from_id() to look up cgroups via id,
   from Tejun Heo.

9) Extend libbpf to support users manually attaching kprobes/uprobes
   in the legacy/perf/link mode, from Menglong Dong.

10) Implement workarounds in the mips BPF JIT for DADDI/R4000,
   from Jiaxun Yang.

11) Enable mixing bpf2bpf and tailcalls for the loongarch BPF JIT,
    from Hengqi Chen.

12) Extend BPF instruction set doc with describing the encoding of BPF
    instructions in terms of how bytes are stored under big/little endian,
    from Jose E. Marchesi.

13) Follow-up to enable kfunc support for riscv BPF JIT, from Pu Lehui.

14) Fix bpf_xdp_query() backwards compatibility on old kernels,
    from Yonghong Song.

15) Fix BPF selftest cross compilation with CLANG_CROSS_FLAGS,
    from Florent Revest.

16) Improve bpf_cpumask_ma to only allocate one bpf_mem_cache,
    from Hou Tao.

17) Fix BPF verifier's check_subprogs to not unnecessarily mark
    a subprogram with has_tail_call, from Ilya Leoshkevich.

18) Fix arm syscall regs spec in libbpf's bpf_tracing.h, from Puranjay Mohan.

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (85 commits)
  selftests/bpf: Add test for legacy/perf kprobe/uprobe attach mode
  selftests/bpf: Split test_attach_probe into multi subtests
  libbpf: Add support to set kprobe/uprobe attach mode
  tools/resolve_btfids: Add /libsubcmd to .gitignore
  bpf: add support for fixed-size memory pointer returns for kfuncs
  bpf: generalize dynptr_get_spi to be usable for iters
  bpf: mark PTR_TO_MEM as non-null register type
  bpf: move kfunc_call_arg_meta higher in the file
  bpf: ensure that r0 is marked scratched after any function call
  bpf: fix visit_insn()'s detection of BPF_FUNC_timer_set_callback helper
  bpf: clean up visit_insn()'s instruction processing
  selftests/bpf: adjust log_fixup's buffer size for proper truncation
  bpf: honor env->test_state_freq flag in is_state_visited()
  selftests/bpf: enhance align selftest's expected log matching
  bpf: improve regsafe() checks for PTR_TO_{MEM,BUF,TP_BUFFER}
  bpf: improve stack slot state printing
  selftests/bpf: Disassembler tests for verifier.c:convert_ctx_access()
  selftests/bpf: test if pointer type is tracked for BPF_ST_MEM
  bpf: allow ctx writes using BPF_ST_MEM instruction
  bpf: Use separate RCU callbacks for freeing selem
  ...
====================

Link: https://lore.kernel.org/r/20230307004346.27578-1-daniel@iogearbox.netSigned-off-by: default avatarJakub Kicinski <kuba@kernel.org>
      36e5e391
  3. 06 Mar, 2023 5 commits
  5. 04 Mar, 2023 16 commits
  7. 03 Mar, 2023 14 commits
    • Kumar Kartikeya Dwivedi's avatar
      bpf: Use separate RCU callbacks for freeing selem · e768e3c5
      Kumar Kartikeya Dwivedi authored 
      Martin suggested that instead of using a byte in the hole (which he has
a use for in his future patch) in bpf_local_storage_elem, we can
dispatch a different call_rcu callback based on whether we need to free
special fields in bpf_local_storage_elem data. The free path, described
in commit 9db44fdd ("bpf: Support kptrs in local storage maps"),
only waits for call_rcu callbacks when there are special (kptrs, etc.)
fields in the map value, hence it is necessary that we only access
smap in this case.

Therefore, dispatch different RCU callbacks based on the BPF map has a
valid btf_record, which dereference and use smap's btf_record only when
it is valid.
Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230303141542.300068-1-memxor@gmail.comSigned-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
      e768e3c5
    • Daniel Borkmann's avatar
      Merge branch 'bpf-kptr-rcu' · db55174d
      Daniel Borkmann authored 
      Alexei Starovoitov says:

====================
v4->v5:
fix typos, add acks.

v3->v4:
- patch 3 got much cleaner after BPF_KPTR_RCU was removed as suggested by David.

- make KF_RCU stronger and require that bpf program checks for NULL
before passing such pointers into kfunc. The prog has to do that anyway
to access fields and it aligns with BTF_TYPE_SAFE_RCU allowlist.

- New patch 6: refactor RCU enforcement in the verifier.
The patches 2,3,6 are part of one feature.
The 2 and 3 alone are incomplete, since RCU pointers are barely useful
without bpf_rcu_read_lock/unlock in GCC compiled kernel.
Even if GCC lands support for btf_type_tag today it will take time
to mandate that version for kernel builds. Hence go with allow list
approach. See patch 6 for details.
This allows to start strict enforcement of TRUSTED | UNTRUSTED
in one part of PTR_TO_BTF_ID accesses.
One step closer to KF_TRUSTED_ARGS by default.

v2->v3:
- Instead of requiring bpf progs to tag fields with __kptr_rcu
teach the verifier to infer RCU properties based on the type.
BPF_KPTR_RCU becomes kernel internal type of struct btf_field.
- Add patch 2 to tag cgroups and dfl_cgrp as trusted.
That bug was spotted by BPF CI on clang compiler kernels,
since patch 3 is doing:
static bool in_rcu_cs(struct bpf_verifier_env *env)
{
        return env->cur_state->active_rcu_lock || !env->prog->aux->sleepable;
}
which makes all non-sleepable programs behave like they have implicit
rcu_read_lock around them. Which is the case in practice.
It was fine on gcc compiled kernels where task->cgroup deference was producing
PTR_TO_BTF_ID, but on clang compiled kernels task->cgroup deference was
producing PTR_TO_BTF_ID | MEM_RCU | MAYBE_NULL, which is more correct,
but selftests were failing. Patch 2 fixes this discrepancy.
With few more patches like patch 2 we can make KF_TRUSTED_ARGS default
for kfuncs and helpers.
- Add comment in selftest patch 5 that it's verifier only check.

v1->v2:
Instead of agressively allow dereferenced kptr_rcu pointers into KF_TRUSTED_ARGS
kfuncs only allow them into KF_RCU funcs.
The KF_RCU flag is a weaker version of KF_TRUSTED_ARGS. The kfuncs marked with
KF_RCU expect either PTR_TRUSTED or MEM_RCU arguments. The verifier guarantees
that the objects are valid and there is no use-after-free, but the pointers
maybe NULL and pointee object's reference count could have reached zero, hence
kfuncs must do != NULL check and consider refcnt==0 case when accessing such
arguments.
No changes in patch 1.
Patches 2,3,4 adjusted with above behavior.

v1:
The __kptr_ref turned out to be too limited, since any "trusted" pointer access
requires bpf_kptr_xchg() which is impractical when the same pointer needs
to be dereferenced by multiple cpus.
The __kptr "untrusted" only access isn't very useful in practice.
Rename __kptr to __kptr_untrusted with eventual goal to deprecate it,
and rename __kptr_ref to __kptr, since that looks to be more common use of kptrs.
Introduce __kptr_rcu that can be directly dereferenced and used similar
to native kernel C code.
Once bpf_cpumask and task_struct kfuncs are converted to observe RCU GP
when refcnt goes to zero, both __kptr and __kptr_untrusted can be deprecated
and __kptr_rcu can become the only __kptr tag.
====================
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
      db55174d
    • Alexei Starovoitov's avatar
      bpf: Refactor RCU enforcement in the verifier. · 6fcd486b
      Alexei Starovoitov authored 
      bpf_rcu_read_lock/unlock() are only available in clang compiled kernels. Lack
of such key mechanism makes it impossible for sleepable bpf programs to use RCU
pointers.

Allow bpf_rcu_read_lock/unlock() in GCC compiled kernels (though GCC doesn't
support btf_type_tag yet) and allowlist certain field dereferences in important
data structures like tast_struct, cgroup, socket that are used by sleepable
programs either as RCU pointer or full trusted pointer (which is valid outside
of RCU CS). Use BTF_TYPE_SAFE_RCU and BTF_TYPE_SAFE_TRUSTED macros for such
tagging. They will be removed once GCC supports btf_type_tag.

With that refactor check_ptr_to_btf_access(). Make it strict in enforcing
PTR_TRUSTED and PTR_UNTRUSTED while deprecating old PTR_TO_BTF_ID without
modifier flags. There is a chance that this strict enforcement might break
existing programs (especially on GCC compiled kernels), but this cleanup has to
start sooner than later. Note PTR_TO_CTX access still yields old deprecated
PTR_TO_BTF_ID. Once it's converted to strict PTR_TRUSTED or PTR_UNTRUSTED the
kfuncs and helpers will be able to default to KF_TRUSTED_ARGS. KF_RCU will
remain as a weaker version of KF_TRUSTED_ARGS where obj refcnt could be 0.

Adjust rcu_read_lock selftest to run on gcc and clang compiled kernels.
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-7-alexei.starovoitov@gmail.com
      6fcd486b
    • Alexei Starovoitov's avatar
      selftests/bpf: Tweak cgroup kfunc test. · 0047d834
      Alexei Starovoitov authored 
      Adjust cgroup kfunc test to dereference RCU protected cgroup pointer
as PTR_TRUSTED and pass into KF_TRUSTED_ARGS kfunc.
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-6-alexei.starovoitov@gmail.com
      0047d834
    • Alexei Starovoitov's avatar
      selftests/bpf: Add a test case for kptr_rcu. · 838bd4ac
      Alexei Starovoitov authored 
      Tweak existing map_kptr test to check kptr_rcu.
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-5-alexei.starovoitov@gmail.com
      838bd4ac
    • Alexei Starovoitov's avatar
      bpf: Introduce kptr_rcu. · 20c09d92
      Alexei Starovoitov authored 
      The life time of certain kernel structures like 'struct cgroup' is protected by RCU.
Hence it's safe to dereference them directly from __kptr tagged pointers in bpf maps.
The resulting pointer is MEM_RCU and can be passed to kfuncs that expect KF_RCU.
Derefrence of other kptr-s returns PTR_UNTRUSTED.

For example:
struct map_value {
   struct cgroup __kptr *cgrp;
};

SEC("tp_btf/cgroup_mkdir")
int BPF_PROG(test_cgrp_get_ancestors, struct cgroup *cgrp_arg, const char *path)
{
  struct cgroup *cg, *cg2;

  cg = bpf_cgroup_acquire(cgrp_arg); // cg is PTR_TRUSTED and ref_obj_id > 0
  bpf_kptr_xchg(&v->cgrp, cg);

  cg2 = v->cgrp; // This is new feature introduced by this patch.
  // cg2 is PTR_MAYBE_NULL | MEM_RCU.
  // When cg2 != NULL, it's a valid cgroup, but its percpu_ref could be zero

  if (cg2)
    bpf_cgroup_ancestor(cg2, level); // safe to do.
}
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-4-alexei.starovoitov@gmail.com
      20c09d92
    • Alexei Starovoitov's avatar
      bpf: Mark cgroups and dfl_cgrp fields as trusted. · 8d093b4e
      Alexei Starovoitov authored 
      bpf programs sometimes do:
bpf_cgrp_storage_get(&map, task->cgroups->dfl_cgrp, ...);
It is safe to do, because cgroups->dfl_cgrp pointer is set diring init and
never changes. The task->cgroups is also never NULL. It is also set during init
and will change when task switches cgroups. For any trusted task pointer
dereference of cgroups and dfl_cgrp should yield trusted pointers. The verifier
wasn't aware of this. Hence in gcc compiled kernels task->cgroups dereference
was producing PTR_TO_BTF_ID without modifiers while in clang compiled kernels
the verifier recognizes __rcu tag in cgroups field and produces
PTR_TO_BTF_ID | MEM_RCU | MAYBE_NULL.
Tag cgroups and dfl_cgrp as trusted to equalize clang and gcc behavior.
When GCC supports btf_type_tag such tagging will done directly in the type.
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/bpf/20230303041446.3630-3-alexei.starovoitov@gmail.com
      8d093b4e
    • Alexei Starovoitov's avatar
      bpf: Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted. · 03b77e17
      Alexei Starovoitov authored 
      __kptr meant to store PTR_UNTRUSTED kernel pointers inside bpf maps.
The concept felt useful, but didn't get much traction,
since bpf_rdonly_cast() was added soon after and bpf programs received
a simpler way to access PTR_UNTRUSTED kernel pointers
without going through restrictive __kptr usage.

Rename __kptr_ref -> __kptr and __kptr -> __kptr_untrusted to indicate
its intended usage.
The main goal of __kptr_untrusted was to read/write such pointers
directly while bpf_kptr_xchg was a mechanism to access refcnted
kernel pointers. The next patch will allow RCU protected __kptr access
with direct read. At that point __kptr_untrusted will be deprecated.
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-2-alexei.starovoitov@gmail.com
      03b77e17
    • Tero Kristo's avatar
      selftests/bpf: Add absolute timer test · 944459e8
      Tero Kristo authored 
      Add test for the absolute BPF timer under the existing timer tests. This
will run the timer two times with 1us expiration time, and then re-arm
the timer at ~35s in the future. At the end, it is verified that the
absolute timer expired exactly two times.
Signed-off-by: default avatarTero Kristo <tero.kristo@linux.intel.com>
Link: https://lore.kernel.org/r/20230302114614.2985072-3-tero.kristo@linux.intel.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      944459e8
    • Tero Kristo's avatar
      bpf: Add support for absolute value BPF timers · f71f8530
      Tero Kristo authored 
      Add a new flag BPF_F_TIMER_ABS that can be passed to bpf_timer_start()
to start an absolute value timer instead of the default relative value.
This makes the timer expire at an exact point in time, instead of a time
with latencies induced by both the BPF and timer subsystems.
Suggested-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: default avatarTero Kristo <tero.kristo@linux.intel.com>
Link: https://lore.kernel.org/r/20230302114614.2985072-2-tero.kristo@linux.intel.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      f71f8530
    • Dave Marchevsky's avatar
      selftests/bpf: Add -Wuninitialized flag to bpf prog flags · ec97a76f
      Dave Marchevsky authored 
      Per C99 standard [0], Section 6.7.8, Paragraph 10:

  If an object that has automatic storage duration is not initialized
  explicitly, its value is indeterminate.

And in the same document, in appendix "J.2 Undefined behavior":

  The behavior is undefined in the following circumstances:
  [...]
  The value of an object with automatic storage duration is used while
  it is indeterminate (6.2.4, 6.7.8, 6.8).

This means that use of an uninitialized stack variable is undefined
behavior, and therefore that clang can choose to do a variety of scary
things, such as not generating bytecode for "bunch of useful code" in
the below example:

  void some_func()
  {
    int i;
    if (!i)
      return;
    // bunch of useful code
  }

To add insult to injury, if some_func above is a helper function for
some BPF program, clang can choose to not generate an "exit" insn,
causing verifier to fail with "last insn is not an exit or jmp". Going
from that verification failure to the root cause of uninitialized use
is certain to be frustrating.

This patch adds -Wuninitialized to the cflags for selftest BPF progs and
fixes up existing instances of uninitialized use.

  [0]: https://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdfSigned-off-by: default avatarDave Marchevsky <davemarchevsky@fb.com>
Cc: David Vernet <void@manifault.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230303005500.1614874-1-davemarchevsky@fb.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      ec97a76f
    • Tejun Heo's avatar
      bpf: Make bpf_get_current_[ancestor_]cgroup_id() available for all program types · c501bf55
      Tejun Heo authored 
      These helpers are safe to call from any context and there's no reason to
restrict access to them. Remove them from bpf_trace and filter lists and add
to bpf_base_func_proto() under perfmon_capable().

v2: After consulting with Andrii, relocated in bpf_base_func_proto() so that
    they require bpf_capable() but not perfomon_capable() as it doesn't read
    from or affect others on the system.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/ZAD8QyoszMZiTzBY@slm.duckdns.orgSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      c501bf55
    • David Vernet's avatar
      bpf, docs: Fix final bpf docs build failure · cacad346
      David Vernet authored 
      maps.rst in the BPF documentation links to the
/userspace-api/ebpf/syscall document
(Documentation/userspace-api/ebpf/syscall.rst). For some reason, if you
try to reference the document with :doc:, the docs build emits the
following warning:

./Documentation/bpf/maps.rst:13: WARNING: \
    unknown document: '/userspace-api/ebpf/syscall'

It appears that other places in the docs tree also don't support using
:doc:. Elsewhere in the BPF documentation, we just reference the kernel
docs page directly. Let's do that here to clean up the last remaining
noise in the docs build.
Signed-off-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230302183918.54190-2-void@manifault.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      cacad346
    • David Vernet's avatar
      bpf, docs: Fix link to netdev-FAQ target · d56b0c46
      David Vernet authored 
      The BPF devel Q&A documentation page makes frequent reference to the
netdev-QA page via the netdev-FAQ rst link. This link is currently
broken, as is evidenced by the build output when making BPF docs:

./Documentation/bpf/bpf_devel_QA.rst:150: WARNING: undefined label: 'netdev-faq'
./Documentation/bpf/bpf_devel_QA.rst:206: WARNING: undefined label: 'netdev-faq'
./Documentation/bpf/bpf_devel_QA.rst:231: WARNING: undefined label: 'netdev-faq'
./Documentation/bpf/bpf_devel_QA.rst:396: WARNING: undefined label: 'netdev-faq'
./Documentation/bpf/bpf_devel_QA.rst:412: WARNING: undefined label: 'netdev-faq'

Fix the links to point to the actual netdev-faq page.
Signed-off-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230302183918.54190-1-void@manifault.comSigned-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      d56b0c46
  9. 02 Mar, 2023 1 commit
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