Re: [RFC 0/2] arm64: kprobes: Fix single-step fault and reentry handling

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

On Wed, 1 Jul 2026 12:14:54 +0000
Pu Hu <hupu@transsion.com> wrote:

> From: hupu <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.
> 
> 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")

Good catch!! 
The series looks good to me.

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

But it should be reviewed by arm64 maintainers too.

BTW, if you are "Pu Hu", the Signed-off-by tag should be
"Pu Hu <...>" instead of "hupu <...>".

Thank you,

> 
> 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
> 
> Before this series, the crash reproduced frequently. With both patches
> applied, it was no longer reproduced in our testing.
> 
> hupu (2):
>   arm64: kprobes: Do not handle non-XOL faults as kprobe faults
>   arm64: kprobes: Allow reentering kprobes while single-stepping
> 
>  arch/arm64/kernel/probes/kprobes.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> -- 
> 2.43.0
> 
> 


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