s390/extable: add EX_TABLE_UA_LOAD_REGPAIR() macro

Add new exception table type which is able to handle register
pairs. If an exception is recognized on such an instruction the
specified register pair will be zeroed, and the specified error
register will be modified so it contains -EFAULT, similar to the
existing EX_TABLE_UA_LOAD_REG() macro.

Link: https://lore.kernel.org/r/Y2J8RSW2khWLgpPo@osirisSigned-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/asm-extable.h

@@ -12,6 +12,7 @@
 #define EX_TYPE_UA_STORE	3
 #define EX_TYPE_UA_LOAD_MEM	4
 #define EX_TYPE_UA_LOAD_REG	5
+#define EX_TYPE_UA_LOAD_REGPAIR	6
 
 #define EX_DATA_REG_ERR_SHIFT	0
 #define EX_DATA_REG_ERR		GENMASK(3, 0)
@@ -85,4 +86,7 @@
 #define EX_TABLE_UA_LOAD_REG(_fault, _target, _regerr, _regzero)	\
 	__EX_TABLE_UA(__ex_table, _fault, _target, EX_TYPE_UA_LOAD_REG, _regerr, _regzero, 0)
 
+#define EX_TABLE_UA_LOAD_REGPAIR(_fault, _target, _regerr, _regzero)	\
+	__EX_TABLE_UA(__ex_table, _fault, _target, EX_TYPE_UA_LOAD_REGPAIR, _regerr, _regzero, 0)
+
 #endif /* __ASM_EXTABLE_H */

arch/s390/mm/extable.c

@@ -47,13 +47,16 @@ static bool ex_handler_ua_load_mem(const struct exception_table_entry *ex, struc
 	return true;
 }
 
-static bool ex_handler_ua_load_reg(const struct exception_table_entry *ex, struct pt_regs *regs)
+static bool ex_handler_ua_load_reg(const struct exception_table_entry *ex,
+				   bool pair, struct pt_regs *regs)
 {
 	unsigned int reg_zero = FIELD_GET(EX_DATA_REG_ADDR, ex->data);
 	unsigned int reg_err = FIELD_GET(EX_DATA_REG_ERR, ex->data);
 
 	regs->gprs[reg_err] = -EFAULT;
 	regs->gprs[reg_zero] = 0;
+	if (pair)
+		regs->gprs[reg_zero + 1] = 0;
 	regs->psw.addr = extable_fixup(ex);
 	return true;
 }
@@ -75,7 +78,9 @@ bool fixup_exception(struct pt_regs *regs)
 	case EX_TYPE_UA_LOAD_MEM:
 		return ex_handler_ua_load_mem(ex, regs);
 	case EX_TYPE_UA_LOAD_REG:
-		return ex_handler_ua_load_reg(ex, regs);
+		return ex_handler_ua_load_reg(ex, false, regs);
+	case EX_TYPE_UA_LOAD_REGPAIR:
+		return ex_handler_ua_load_reg(ex, true, regs);
 	}
 	panic("invalid exception table entry");
 }