arm64: Simplify do_notify_resume() DAIF masking

In do_notify_resume, we handle _TIF_NEED_RESCHED differently from all
other flags, leaving IRQ+FIQ masked when calling into schedule(). This
masking is a historical artifact, and it is not currently necessary
to mask IRQ+FIQ when calling into schedule (as evidenced by the generic
exit_to_user_mode_loop(), which unmasks IRQs before checking
_TIF_NEED_RESCHED and calling schedule()).

This patch removes the special case for _TIF_NEED_RESCHED, moving this
check into the main loop such that schedule() will be called from a
regular process context with IRQ+FIQ unmasked. This is a minor
simplification to do_notify_resume() and brings it into line with the
generic exit_to_user_mode_loop() logic. This will also aid subsequent
rework of DAIF management.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240206123848.1696480-2-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Itaru Kitayama <itaru.kitayama@linux.dev>

Author: mrutland-arm

arch/arm64/kernel/signal.c

@@ -1281,32 +1281,28 @@ static void do_signal(struct pt_regs *regs)
 void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
 {
 	do {
-		if (thread_flags & _TIF_NEED_RESCHED) {
-			/* Unmask Debug and SError for the next task */
-			local_daif_restore(DAIF_PROCCTX_NOIRQ);
+		local_daif_restore(DAIF_PROCCTX);
 
+		if (thread_flags & _TIF_NEED_RESCHED)
 			schedule();
-		} else {
-			local_daif_restore(DAIF_PROCCTX);
 
-			if (thread_flags & _TIF_UPROBE)
-				uprobe_notify_resume(regs);
+		if (thread_flags & _TIF_UPROBE)
+			uprobe_notify_resume(regs);
 
-			if (thread_flags & _TIF_MTE_ASYNC_FAULT) {
-				clear_thread_flag(TIF_MTE_ASYNC_FAULT);
-				send_sig_fault(SIGSEGV, SEGV_MTEAERR,
-					       (void __user *)NULL, current);
-			}
+		if (thread_flags & _TIF_MTE_ASYNC_FAULT) {
+			clear_thread_flag(TIF_MTE_ASYNC_FAULT);
+			send_sig_fault(SIGSEGV, SEGV_MTEAERR,
+				       (void __user *)NULL, current);
+		}
 
-			if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
-				do_signal(regs);
+		if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
+			do_signal(regs);
 
-			if (thread_flags & _TIF_NOTIFY_RESUME)
-				resume_user_mode_work(regs);
+		if (thread_flags & _TIF_NOTIFY_RESUME)
+			resume_user_mode_work(regs);
 
-			if (thread_flags & _TIF_FOREIGN_FPSTATE)
-				fpsimd_restore_current_state();
-		}
+		if (thread_flags & _TIF_FOREIGN_FPSTATE)
+			fpsimd_restore_current_state();
 
 		local_daif_mask();
 		thread_flags = read_thread_flags();