[S390] addressing mode limits and psw address wrapping

An instruction with an address right below the adress limit for the
current addressing mode will wrap. The instruction restart logic in
the protection fault handler and the signal code need to follow the
wrapping rules to find the correct instruction address.

Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/include/asm/processor.h

···
  * Set PSW mask to specified value, while leaving the
  * PSW addr pointing to the next instruction.
  */
-
 static inline void __load_psw_mask (unsigned long mask)
 {
 	unsigned long addr;
···
 		"1:"
 		: "=&d" (addr), "=Q" (psw) : "Q" (psw) : "memory", "cc");
 #endif /* __s390x__ */
+}
+
+/*
+ * Rewind PSW instruction address by specified number of bytes.
+ */
+static inline unsigned long __rewind_psw(psw_t psw, unsigned long ilc)
+{
+#ifndef __s390x__
+	if (psw.addr & PSW_ADDR_AMODE)
+		/* 31 bit mode */
+		return (psw.addr - ilc) | PSW_ADDR_AMODE;
+	/* 24 bit mode */
+	return (psw.addr - ilc) & ((1UL << 24) - 1);
+#else
+	unsigned long mask;
+
+	mask = (psw.mask & PSW_MASK_EA) ? -1UL :
+	       (psw.mask & PSW_MASK_BA) ? (1UL << 31) - 1 :
+					  (1UL << 24) - 1;
+	return (psw.addr - ilc) & mask;
+#endif
 }
  
 /*

arch/s390/include/asm/ptrace.h

···
 #define PSW_MASK_ASC		0x0000C000UL
 #define PSW_MASK_CC		0x00003000UL
 #define PSW_MASK_PM		0x00000F00UL
+#define PSW_MASK_EA		0x00000000UL
+#define PSW_MASK_BA		0x00000000UL
 
 #define PSW_ADDR_AMODE		0x80000000UL
 #define PSW_ADDR_INSN		0x7FFFFFFFUL
···
 #define PSW_MASK_ASC		0x0000C00000000000UL
 #define PSW_MASK_CC		0x0000300000000000UL
 #define PSW_MASK_PM		0x00000F0000000000UL
+#define PSW_MASK_EA		0x0000000100000000UL
+#define PSW_MASK_BA		0x0000000080000000UL
 
 #define PSW_ADDR_AMODE		0x0000000000000000UL
 #define PSW_ADDR_INSN		0xFFFFFFFFFFFFFFFFUL

arch/s390/kernel/signal.c

···
 			/* fallthrough */
 			case -ERESTARTNOINTR:
 				regs->gprs[2] = regs->orig_gpr2;
-				regs->psw.addr = regs->psw.addr -
-					(regs->svc_code >> 16);
+				regs->psw.addr =
+					__rewind_psw(regs->psw,
+						     regs->svc_code >> 16);
 				break;
 			}
 			/* No longer in a system call */

arch/s390/mm/fault.c

···
 	int fault;
 
 	/* Protection exception is suppressing, decrement psw address. */
-	regs->psw.addr -= (pgm_int_code >> 16);
+	regs->psw.addr = __rewind_psw(regs->psw, pgm_int_code >> 16);
 	/*
 	 * Check for low-address protection.  This needs to be treated
 	 * as a special case because the translation exception code