For an architecture to enable CONFIG_ARCH_HAS_RESCHED_LAZY, two things are required: 1) Adding a TIF_NEED_RESCHED_LAZY flag definition 2) Checking for TIF_NEED_RESCHED_LAZY in the appropriate locations 2) is handled in a generic manner by CONFIG_GENERIC_ENTRY, which isn't (yet) implemented for arm64. However, outside of core scheduler code, TIF_NEED_RESCHED_LAZY only needs to be checked on a kernel exit, meaning: o return/entry to userspace. o return/entry to guest. The return/entry to a guest is all handled by xfer_to_guest_mode_handle_work() which already does the right thing, so it can be left as-is. arm64 doesn't use common entry's exit_to_user_mode_prepare(), so update its return to user path to check for TIF_NEED_RESCHED_LAZY and call into schedule() accordingly. Link: https://lore.kernel.org/linux-rt-users/20241216190451.1c61977c@mordecai.tesarici.cz/ Link: https://lore.kernel.org/all/xhsmh4j0fl0p3.mognet@vschneid-thinkpadt14sgen2i.remote.csb/ Signed-off-by: Mark Rutland <mark.rutland@arm.com> [testdrive, _TIF_WORK_MASK fixlet and changelog.] Signed-off-by: Mike Galbraith <efault@gmx.de> [Another round of testing; changelog faff] Signed-off-by: Valentin Schneider <vschneid@redhat.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>