powerpc/interrupts: Fix kuep_unlock() call

Same as kuap_user_restore(), kuep_unlock() has to be called when
really returning to user, that is in interrupt_exit_user_prepare(),
not in interrupt_exit_prepare().

Fixes: b5efec00b6 ("powerpc/32s: Move KUEP locking/unlocking in C")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b831e54a2579db24fbef836ed415588ce2b3e825.1620312573.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/interrupt.h

@@ -153,8 +153,6 @@ static inline void interrupt_enter_prepare(struct pt_regs *regs, struct interrup
  */
 static inline void interrupt_exit_prepare(struct pt_regs *regs, struct interrupt_state *state)
 {
-	if (user_mode(regs))
-		kuep_unlock();
 }
 
 static inline void interrupt_async_enter_prepare(struct pt_regs *regs, struct interrupt_state *state)

arch/powerpc/kernel/interrupt.c

@@ -427,6 +427,7 @@ again:
 
 	/* Restore user access locks last */
 	kuap_user_restore(regs);
+	kuep_unlock();
 
 	return ret;
 }