[PATCH v3 bpf-next 0/3] Add bpf_access_process_vm helper and sleepable bpf iterator programs

[Kenny Yu <kennyyu@fb.com>]

This patch series makes the following changes:
* Adds a new bpf helper `bpf_access_process_vm` to read user space
  memory from a different task.
* Adds the ability to create sleepable bpf iterator programs.

As an example of how this will be used, at Meta we are using bpf task
iterator programs and this new bpf helper to read C++ async stack traces of
a running process for debugging C++ binaries in production.

Changes since v2:
* Reorder arguments in `bpf_access_process_vm` to match existing related
  bpf helpers (e.g. `bpf_probe_read_kernel`, `bpf_probe_read_user`,
  `bpf_copy_from_user`).
* `flags` argument is provided for future extensibility and is not
  currently used, and we always invoke `access_process_vm` with no flags.
* Merge bpf helper patch and `bpf_iter_run_prog` patch together for better
  bisectability in case of failures.
* Clean up formatting and comments in selftests.

Changes since v1:
* Fixed "Invalid wait context" issue in `bpf_iter_run_prog` by using
  `rcu_read_lock_trace()` for sleepable bpf iterator programs.

Kenny Yu (3):
  bpf: Add bpf_access_process_vm() helper
  libbpf: Add "iter.s" section for sleepable bpf iterator programs
  selftests/bpf: Add test for sleepable bpf iterator programs

 include/linux/bpf.h                           |  1 +
 include/uapi/linux/bpf.h                      | 10 +++++
 kernel/bpf/bpf_iter.c                         | 20 ++++++---
 kernel/bpf/helpers.c                          | 19 ++++++++
 kernel/trace/bpf_trace.c                      |  2 +
 tools/include/uapi/linux/bpf.h                | 10 +++++
 tools/lib/bpf/libbpf.c                        |  1 +
 .../selftests/bpf/prog_tests/bpf_iter.c       | 16 +++++++
 .../selftests/bpf/progs/bpf_iter_task.c       | 43 +++++++++++++++++++
 9 files changed, 117 insertions(+), 5 deletions(-)

-- 
2.30.2