s390/signal: always restore saved runtime instrumentation psw bit

Commit "s390: fix handling of runtime instrumentation psw bit" (5ebf250d)
changed the behavior of setting the runtime instrumentation psw bit.  This
commit restores the original logic:

1. When returning from the signal handler, the runtime instrumentation psw bit
   is restored to its saved state.
2. If the runtime instrumentation psw bit is enabled during the signal handler,
   it is always turned off when leaving the signal handler.  The saved state
   is restored as described in 1.  That also implies that turning on runtime
   instrumentation in the signal handler is only effective while running in the
   signal context.
Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>

arch/s390/kernel/compat_signal.c

@@ -194,7 +194,7 @@ static int restore_sigregs32(struct pt_regs *regs,_sigregs32 __user *sregs)
 		return -EINVAL;
 
 	/* Use regs->psw.mask instead of PSW_USER_BITS to preserve PER bit. */
-	regs->psw.mask = (regs->psw.mask & ~PSW_MASK_USER) |
+	regs->psw.mask = (regs->psw.mask & ~(PSW_MASK_USER | PSW_MASK_RI)) |
 		(__u64)(user_sregs.regs.psw.mask & PSW32_MASK_USER) << 32 |
 		(__u64)(user_sregs.regs.psw.mask & PSW32_MASK_RI) << 32 |
 		(__u64)(user_sregs.regs.psw.addr & PSW32_ADDR_AMODE);

arch/s390/kernel/signal.c

@@ -94,7 +94,7 @@ static int restore_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
 		return -EINVAL;
 
 	/* Use regs->psw.mask instead of PSW_USER_BITS to preserve PER bit. */
-	regs->psw.mask = (regs->psw.mask & ~PSW_MASK_USER) |
+	regs->psw.mask = (regs->psw.mask & ~(PSW_MASK_USER | PSW_MASK_RI)) |
 		(user_sregs.regs.psw.mask & (PSW_MASK_USER | PSW_MASK_RI));
 	/* Check for invalid user address space control. */
 	if ((regs->psw.mask & PSW_MASK_ASC) == PSW_ASC_HOME)