Re: [PATCHv4 bpf-next 0/7] uprobe: uretprobe speed up

[Andrii Nakryiko]

On Thu, May 2, 2024 at 5:23 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> hi,
> as part of the effort on speeding up the uprobes [0] coming with
> return uprobe optimization by using syscall instead of the trap
> on the uretprobe trampoline.
>
> The speed up depends on instruction type that uprobe is installed
> and depends on specific HW type, please check patch 1 for details.
>
> Patches 1-6 are based on bpf-next/master, but path 1 and 2 are
> apply-able on linux-trace.git tree probes/for-next branch.
> Patch 7 is based on man-pages master.
>
> v4 changes:
>   - added acks [Oleg,Andrii,Masami]
>   - reworded the man page and adding more info to NOTE section [Masami]
>   - rewrote bpf tests not to use trace_pipe [Andrii]
>   - cc-ed linux-man list
>
> Also available at:
>   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   uretprobe_syscall
>

It looks great to me, thanks! Unfortunately BPF CI build is broken,
probably due to some of the Makefile additions, please investigate and
fix (or we'll need to fix something on BPF CI side), but it looks like
you'll need another revision, unfortunately.

pw-bot: cr

  [0] https://github.com/kernel-patches/bpf/actions/runs/8923849088/job/24509002194



But while we are at it.

Masami, Oleg,

What should be the logistics of landing this? Can/should we route this
through the bpf-next tree, given there are lots of BPF-based
selftests? Or you want to take this through
linux-trace/probes/for-next? In the latter case, it's probably better
to apply only the first two patches to probes/for-next and the rest
should still go through the bpf-next tree (otherwise we are running
into conflicts in BPF selftests). Previously we were handling such
cross-tree dependencies by creating a named branch or tag, and merging
it into bpf-next (so that all SHAs are preserved). It's a bunch of
extra work for everyone involved, so the simplest way would be to just
land through bpf-next, of course. But let me know your preferences.

Thanks!

> thanks,
> jirka
>
>
> Notes to check list items in Documentation/process/adding-syscalls.rst:
>
> - System Call Alternatives
>   New syscall seems like the best way in here, becase we need

typo (thanks, Gmail): because

>   just to quickly enter kernel with no extra arguments processing,
>   which we'd need to do if we decided to use another syscall.
>
> - Designing the API: Planning for Extension
>   The uretprobe syscall is very specific and most likely won't be
>   extended in the future.
>
>   At the moment it does not take any arguments and even if it does
>   in future, it's allowed to be called only from trampoline prepared
>   by kernel, so there'll be no broken user.
>
> - Designing the API: Other Considerations
>   N/A because uretprobe syscall does not return reference to kernel
>   object.
>
> - Proposing the API
>   Wiring up of the uretprobe system call si in separate change,

typo: is

>   selftests and man page changes are part of the patchset.
>
> - Generic System Call Implementation
>   There's no CONFIG option for the new functionality because it
>   keeps the same behaviour from the user POV.
>
> - x86 System Call Implementation
>   It's 64-bit syscall only.
>
> - Compatibility System Calls (Generic)
>   N/A uretprobe syscall has no arguments and is not supported
>   for compat processes.
>
> - Compatibility System Calls (x86)
>   N/A uretprobe syscall is not supported for compat processes.
>
> - System Calls Returning Elsewhere
>   N/A.
>
> - Other Details
>   N/A.
>
> - Testing
>   Adding new bpf selftests and ran ltp on top of this change.
>
> - Man Page
>   Attached.
>
> - Do not call System Calls in the Kernel
>   N/A.
>
>
> [0] https://lore.kernel.org/bpf/ZeCXHKJ--iYYbmLj@krava/
> ---
> Jiri Olsa (6):
>       uprobe: Wire up uretprobe system call
>       uprobe: Add uretprobe syscall to speed up return probe
>       selftests/bpf: Add uretprobe syscall test for regs integrity
>       selftests/bpf: Add uretprobe syscall test for regs changes
>       selftests/bpf: Add uretprobe syscall call from user space test
>       selftests/bpf: Add uretprobe compat test
>
>  arch/x86/entry/syscalls/syscall_64.tbl                      |   1 +
>  arch/x86/kernel/uprobes.c                                   | 115 ++++++++++++++++++++++++++++
>  include/linux/syscalls.h                                    |   2 +
>  include/linux/uprobes.h                                     |   3 +
>  include/uapi/asm-generic/unistd.h                           |   5 +-
>  kernel/events/uprobes.c                                     |  24 ++++--
>  kernel/sys_ni.c                                             |   2 +
>  tools/include/linux/compiler.h                              |   4 +
>  tools/testing/selftests/bpf/.gitignore                      |   1 +
>  tools/testing/selftests/bpf/Makefile                        |   7 +-
>  tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c       | 123 ++++++++++++++++++++++++++++-
>  tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c     | 382 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/uprobe_syscall.c          |  15 ++++
>  tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c |  17 +++++
>  14 files changed, 691 insertions(+), 10 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/uprobe_syscallc
>  create mode 100644 tools/testing/selftests/bpf/progs/uprobe_syscall.c
>  create mode 100644 tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c
>
> Jiri Olsa (1):
>       man2: Add uretprobe syscall page
>
>  man2/uretprobe.2 | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
>  create mode 100644 man2/uretprobe.2