Re: [RFC 0/3] arm64: kprobes: Fix single-step fault and reentry handling

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi, Pu,

Thanks for updating the series. But even if it just update
the signed-off-by, please update the version.

Also, can you check the Sashiko's comments?

https://sashiko.dev/#/patchset/20260706083636.159883-1-hupu%40transsion.com

Thank you,

On Mon, 6 Jul 2026 08:36:46 +0000
Pu Hu <hupu@transsion.com> wrote:

> From: Pu Hu <hupu@transsion.com>
> 
> This series fixes two arm64 kprobes issues observed when running
> simpleperf with preemptirq tracepoints and dwarf callchains while a
> kprobe is active on a frequently executed kernel function.
> 
> The crash happens in the kprobe debug exception path. While a kprobe is
> preparing or executing its XOL single-step instruction, perf/trace code
> can run in the same window. That code may either take a fault of its own
> or hit another kprobe.
> 
> Patch 1 makes kprobe_fault_handler() handle a fault in
> KPROBE_HIT_SS/KPROBE_REENTER only when the faulting PC points at the
> current kprobe's XOL instruction. Otherwise the fault is left to the
> normal fault handling path.
> 
> Patch 2 allows a kprobe hit in KPROBE_HIT_SS to be handled as a
> recoverable one-level reentry. Only a hit while already in
> KPROBE_REENTER remains unrecoverable.
> 
> Patch 3 adds a kprobes selftest which registers a kprobe on a frequently
> executed filemap fault path and drives repeated file-backed page faults
> from userspace. This provides a smaller reproducer for validating the
> fault handling fix.
> 
> This follows the same logic as the existing x86 fixes:
>   6381c24cd6d5 ("kprobes/x86: Fix page-fault handling logic")
>   6a5022a56ac3 ("kprobes/x86: Allow to handle reentered kprobe on single-stepping")
> 
> Reproducer:
> 
>   simpleperf record -p <pid> -f 10000 \
>     -e preemptirq:preempt_disable \
>     -e preemptirq:preempt_enable \
>     --duration 9 --call-graph dwarf \
>     -o /data/local/tmp/perf.data
> 
> The new selftest can be built from tools/testing/selftests/kprobe/ and
> used to exercise the page fault handling path with the test kprobe
> module loaded.
> 
> Before this series, the crash reproduced frequently. With both patches
> applied, it was no longer reproduced in our testing.
> 
> 
> Pu Hu (3):
>   arm64: kprobes: Do not handle non-XOL faults as kprobe faults
>   arm64: kprobes: Allow reentering kprobes while single-stepping
>   selftests/kprobes: Add kprobe stress test for page fault handling
> 
>  arch/arm64/kernel/probes/kprobes.c            |  22 +++-
>  tools/testing/selftests/kprobe/.gitignore     |   2 +
>  tools/testing/selftests/kprobe/Makefile       |  75 +++++++++++++
>  tools/testing/selftests/kprobe/fault_stress.c | 105 ++++++++++++++++++
>  .../selftests/kprobe/kprobe_folio_stress.c    |  70 ++++++++++++
>  5 files changed, 273 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/kprobe/.gitignore
>  create mode 100644 tools/testing/selftests/kprobe/Makefile
>  create mode 100644 tools/testing/selftests/kprobe/fault_stress.c
>  create mode 100644 tools/testing/selftests/kprobe/kprobe_folio_stress.c
> 
> -- 
> 2.43.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>