s390/mcck: always enter C handler with DAT enabled

The machine check handler must be entered with DAT disabled
in case control registers are corrupted or a storage error
happened and we can not tell if such error corresponds to a
page table.

Both of described conditions end up in stopping all CPUs and
entering the disabled wait in C half of the handler. However,
the storage errors are still checked after the DAT is enabled
and C code is entered. In case a page table is damaged such
flow is not expected to work.

This update paves the way for moving the storage error checks
from C to assembler half. All fatal errors that can only be
handled with DAT disabled are handled in assembler half also.
As result, the C half is only entered if the DAT is secured.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/entry.S

@@ -570,7 +570,6 @@ ENTRY(mcck_int_handler)
 	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
 .Lmcck_stack:
 	lg	%r15,__LC_MCCK_STACK
-.Lmcck_skip:
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	stctg	%c1,%c1,__PT_CR1(%r11)
 	lctlg	%c1,%c1,__LC_KERNEL_ASCE
@@ -612,8 +611,33 @@ ENTRY(mcck_int_handler)
 	b	__LC_RETURN_MCCK_LPSWE
 
 .Lmcck_panic:
-	lg	%r15,__LC_NODAT_STACK
-	j	.Lmcck_skip
+	/*
+	 * Iterate over all possible CPU addresses in the range 0..0xffff
+	 * and stop each CPU using signal processor. Use compare and swap
+	 * to allow just one CPU-stopper and prevent concurrent CPUs from
+	 * stopping each other while leaving the others running.
+	 */
+	lhi	%r5,0
+	lhi	%r6,1
+	larl	%r7,.Lstop_lock
+	cs	%r5,%r6,0(%r7)		# single CPU-stopper only
+	jnz	4f
+	larl	%r7,.Lthis_cpu
+	stap	0(%r7)			# this CPU address
+	lh	%r4,0(%r7)
+	nilh	%r4,0
+	lhi	%r0,1
+	sll	%r0,16			# CPU counter
+	lhi	%r3,0			# next CPU address
+0:	cr	%r3,%r4
+	je	2f
+1:	sigp	%r1,%r3,SIGP_STOP	# stop next CPU
+	brc	SIGP_CC_BUSY,1b
+2:	ahi	%r3,1
+	brct	%r0,0b
+3:	sigp	%r1,%r4,SIGP_STOP	# stop this CPU
+	brc	SIGP_CC_BUSY,3b
+4:	j	4b
 ENDPROC(mcck_int_handler)
 
 #
@@ -664,6 +688,11 @@ ENTRY(stack_overflow)
 ENDPROC(stack_overflow)
 #endif
 
+	.section .data, "aw"
+		.align	4
+.Lstop_lock:	.long	0
+.Lthis_cpu:	.short	0
+
 	.section .rodata, "a"
 #define SYSCALL(esame,emu)	.quad __s390x_ ## esame
 	.globl	sys_call_table

arch/s390/kernel/nmi.c

@@ -205,14 +205,6 @@ static int notrace s390_check_registers(union mci mci, int umode)
 			s390_handle_damage();
 		kill_task = 1;
 	}
-	/* Check control registers */
-	if (!mci.cr) {
-		/*
-		 * Control registers have unknown contents.
-		 * Can't recover and therefore stopping machine.
-		 */
-		s390_handle_damage();
-	}
 	if (!mci.fp) {
 		/*
 		 * Floating point registers can't be restored. If the
@@ -273,22 +265,6 @@ static int notrace s390_check_registers(union mci mci, int umode)
 			kill_task = 1;
 		}
 	}
-	/* Check if old PSW is valid */
-	if (!mci.wp) {
-		/*
-		 * Can't tell if we come from user or kernel mode
-		 * -> stopping machine.
-		 */
-		s390_handle_damage();
-	}
-	/* Check for invalid kernel instruction address */
-	if (!mci.ia && !umode) {
-		/*
-		 * The instruction address got lost while running
-		 * in the kernel -> stopping machine.
-		 */
-		s390_handle_damage();
-	}
 
 	if (!mci.ms || !mci.pm || !mci.ia)
 		kill_task = 1;
@@ -353,11 +329,6 @@ int notrace s390_do_machine_check(struct pt_regs *regs)
 	mci.val = S390_lowcore.mcck_interruption_code;
 	mcck = this_cpu_ptr(&cpu_mcck);
 
-	if (mci.sd) {
-		/* System damage -> stopping machine */
-		s390_handle_damage();
-	}
-
 	/*
 	 * Reinject the instruction processing damages' machine checks
 	 * including Delayed Access Exception into the guest