Re: [PATCHv8 bpf-next 0/9] uprobe: uretprobe speed up

Andrii Nakryiko
2024-06-12T07:02:38Z

On Tue, Jun 11, 2024 at 3:52 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Tue, 11 Jun 2024 13:21:49 +0200
> Jiri Olsa <jolsa@kernel.org> 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 1-8 are based on bpf-next/master, but patch 2 and 3 are
> > apply-able on linux-trace.git tree probes/for-next branch.
> > Patch 9 is based on man-pages master.
> >
> > v8 changes:
> > - rebased (another new syscall got merged)
> > - added acks
> >
> > Also available at:
> > https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
> > uretprobe_syscall
>
> Applied patch [1/9] - [8/9] on probes/for-next in
> git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
>

Thanks, Masami, looks good! I also confirmed that probes/for-next and
bpf-next/master can be merged with no conflicts (hopefully it stays
this way till the next merge window).

> Thank you!
>
> >
> > 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, because we need
> > 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 is in separate change,
> > 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 (8):
> > x86/shstk: Make return uprobe work with shadow stack
> > uprobe: Wire up uretprobe system call
> > uprobe: Add uretprobe syscall to speed up return probe
> > selftests/x86: Add return uprobe shadow stack test
> > 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 shadow stack test
> >
> > arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> > arch/x86/include/asm/shstk.h | 4 +
> > arch/x86/kernel/shstk.c | 16 ++++
> > arch/x86/kernel/uprobes.c | 124 ++++++++++++++++++++++++++++-
> > 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/bpf_testmod/bpf_testmod.c | 123 ++++++++++++++++++++++++++++-
> > tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c | 385 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > tools/testing/selftests/bpf/progs/uprobe_syscall.c | 15 ++++
> > tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c | 17 ++++
> > tools/testing/selftests/x86/test_shadow_stack.c | 145 ++++++++++++++++++++++++++++++++++
> > 15 files changed, 860 insertions(+), 10 deletions(-)
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c
> > 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
> >
> > man/man2/uretprobe.2 | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 56 insertions(+)
> > create mode 100644 man/man2/uretprobe.2
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>