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

[Ada Couprie Diaz <ada.coupriediaz@arm.com>]

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@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: Linus Walleij <linusw@kernel.org>
> Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---

Reviewed-by: Ada Couprie Diaz <ada.coupriediaz@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 !
Thanks,
Ada