Add sdei_event_signal(), a thin wrapper over the SDEI_EVENT_SIGNAL call (DEN0054) that makes the software-signalled event (event 0) pending on a target PE -- delivered NMI-like even when that PE has interrupts masked. It takes no locks, so it is safe to call from NMI / crash context. Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org> Reviewed-by: Douglas Anderson <dianders@chromium.org> Tested-by: Yin Fengwei <fengwei_yin@linux.alibaba.com> Signed-off-by: Will Deacon <will@kernel.org>