[PATCH v15 08/11] arm64/ptrace: Define and use _TIF_SYSCALL_EXIT_WORK

[Ada Couprie Diaz]

On 25/06/2026 12:41, Jinjie Ruan wrote:
> On 6/24/2026 10:53 PM, Ada Couprie Diaz wrote:
>> On 11/05/2026 10:21, Jinjie Ruan wrote:
>>> Introduce _TIF_SYSCALL_EXIT_WORK to filter out entry-only flags
>>> during the syscall exit path. This aligns arm64 with the generic
>>> entry framework's SYSCALL_WORK_EXIT semantics.
>>>
>>> [Rationale]
>>> The current syscall exit path uses _TIF_SYSCALL_WORK to decide whether
>>> to invoke syscall_exit_work(). However, _TIF_SYSCALL_WORK includes
>>> flags that are only relevant during syscall entry:
>>>
>>> 1. _TIF_SECCOMP: Seccomp filtering (__secure_computing) only runs
>>>     on entry. There is no seccomp callback for syscall exit.
>>>
>>> 2. _TIF_SYSCALL_EMU: In PTRACE_SYSEMU mode, the syscall is
>>>     intercepted and skipped on entry. Since the syscall is never
>>>     executed, reporting a syscall exit stop is unnecessary.
>>>
>>> [Changes]
>>> - Define _TIF_SYSCALL_EXIT_WORK: A new mask containing only flags
>>>     requiring exit processing: _TIF_SYSCALL_TRACE, _TIF_SYSCALL_AUDIT,
>>>     and _TIF_SYSCALL_TRACEPOINT.
>>>
>>> - Update exit path: Use _TIF_SYSCALL_EXIT_WORK in
>>>     syscall_exit_to_user_mode_work() to avoid redundant calls to
>>>     audit and ptrace reporting when only entry-flags are set.
>>>
>>> - Cleanup: Remove the has_syscall_work() helper as it is no longer
>>>     needed. Direct flag comparison is now used to distinguish between
>>>     entry and exit work requirements.
>>>
>>> [Impact]
>>> audit_syscall_exit() and report_syscall_exit() will no longer be
>>> triggered for seccomp-only or emu-only syscalls. This matches the
>>> generic entry behavior and improves efficiency by skipping unnecessary
>>> exit processing.
>>>
>>> Cc: Mark Rutland <mark.rutland at arm.com>
>>> Cc: Will Deacon <will at kernel.org>
>>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>>> Reviewed-by: Linus Walleij <linusw at kernel.org>
>>> Reviewed-by: Yeoreum Yun <yeoreum.yun at arm.com>
>>> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
>>> ---
>> Reviewed-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
>>
>> Definitely not related to this series, but it feels like this brings us
>> quite close to being able to switch to generic TIF flags as well :
>> only TIF_FOREIGN_PSTATE and TIF_MTE_ASYNC_FAULT
>> would need to be moved to the upper 16 bits,
>> with TIF_RESTORE_SIGMASK and TIF_MEMDIE freeing two slots there.
>>
>> Not sure how important the bit number changes would be and if any
>> of the extra generic bits require any arch support (TIF_POLLING_NRFLAG,
>> TIF_USER_RETURN_NOTIFY, TIF_RSEQ, TIF_HRTIMER_REARM)...
>>
>> But again, just thinking out loud !
> Hi Ada,
>
> You have incredible foresight! You are absolutely right that this series
> lays the perfect groundwork for switching arm64 to generic TIF flags
> (HAVE_GENERIC_TIF_BITS).
>
> I am happy to share that I have already implemented exactly what you
> described—including migrating the architecture-specific flags to the
> upper 16 bits and enabling the generic TIF infrastructure—in a separate,
> dedicated patch series.
>
> You can find the implementation and discussion here:
>
> https://lore.kernel.org/all/20260320104222.1381274-1-ruanjinjie@huawei.com/
>
> Since that series directly builds on top of the cleanups and
> infrastructure introduced here, I plan to actively push it forward right
> after we get this core generic entry conversion landed.
>
> Thanks again for looking so far ahead and validating the direction!
>
> Best regards,
> Jinjie

Hi Jinjie,

Oh, neat, I evidently missed this series ;
glad you confirmed I was on the right track !

I am looking forward to seeing both those works merged then :)

Kind regards,
Ada