s390: remove critical section cleanup from entry.S

The current code is rather complex and caused a lot of subtle
and hard to debug bugs in the past. Simplify the code by calling
the system_call handler with interrupts disabled, save
machine state, and re-enable them later.

This requires significant changes to the machine check handling code
as well. When the machine check interrupt arrived while being in kernel
mode the new code will signal pending machine checks with a SIGP external
call. When userspace was interrupted, the handler will switch to the
kernel stack and directly execute s390_handle_mcck().

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: svens-s390

arch/s390/include/asm/nmi.h

@@ -99,7 +99,7 @@ int nmi_alloc_per_cpu(struct lowcore *lc);
 void nmi_free_per_cpu(struct lowcore *lc);
 
 void s390_handle_mcck(void);
-void s390_do_machine_check(struct pt_regs *regs);
+int s390_do_machine_check(struct pt_regs *regs);
 
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_S390_NMI_H */

arch/s390/include/asm/processor.h

@@ -14,17 +14,15 @@
 
 #include <linux/bits.h>
 
-#define CIF_MCCK_PENDING	0	/* machine check handling is pending */
-#define CIF_ASCE_PRIMARY	1	/* primary asce needs fixup / uaccess */
-#define CIF_ASCE_SECONDARY	2	/* secondary asce needs fixup / uaccess */
-#define CIF_NOHZ_DELAY		3	/* delay HZ disable for a tick */
-#define CIF_FPU			4	/* restore FPU registers */
-#define CIF_IGNORE_IRQ		5	/* ignore interrupt (for udelay) */
-#define CIF_ENABLED_WAIT	6	/* in enabled wait state */
-#define CIF_MCCK_GUEST		7	/* machine check happening in guest */
-#define CIF_DEDICATED_CPU	8	/* this CPU is dedicated */
-
-#define _CIF_MCCK_PENDING	BIT(CIF_MCCK_PENDING)
+#define CIF_ASCE_PRIMARY	0	/* primary asce needs fixup / uaccess */
+#define CIF_ASCE_SECONDARY	1	/* secondary asce needs fixup / uaccess */
+#define CIF_NOHZ_DELAY		2	/* delay HZ disable for a tick */
+#define CIF_FPU			3	/* restore FPU registers */
+#define CIF_IGNORE_IRQ		4	/* ignore interrupt (for udelay) */
+#define CIF_ENABLED_WAIT	5	/* in enabled wait state */
+#define CIF_MCCK_GUEST		6	/* machine check happening in guest */
+#define CIF_DEDICATED_CPU	7	/* this CPU is dedicated */
+
 #define _CIF_ASCE_PRIMARY	BIT(CIF_ASCE_PRIMARY)
 #define _CIF_ASCE_SECONDARY	BIT(CIF_ASCE_SECONDARY)
 #define _CIF_NOHZ_DELAY		BIT(CIF_NOHZ_DELAY)