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>

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)

arch/s390/kernel/idle.c

@@ -24,19 +24,19 @@ void enabled_wait(void)
 {
 	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
 	unsigned long long idle_time;
-	unsigned long psw_mask;
+	unsigned long psw_mask, flags;
 
-	trace_hardirqs_on();
 
 	/* Wait for external, I/O or machine check interrupt. */
 	psw_mask = PSW_KERNEL_BITS | PSW_MASK_WAIT | PSW_MASK_DAT |
 		PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK;
 	clear_cpu_flag(CIF_NOHZ_DELAY);
 
+	local_irq_save(flags);
 	/* Call the assembler magic in entry.S */
 	psw_idle(idle, psw_mask);
+	local_irq_restore(flags);
 
-	trace_hardirqs_off();
 
 	/* Account time spent with enabled wait psw loaded as idle time. */
 	write_seqcount_begin(&idle->seqcount);
@@ -118,22 +118,16 @@ u64 arch_cpu_idle_time(int cpu)
 
 void arch_cpu_idle_enter(void)
 {
-	local_mcck_disable();
 }
 
 void arch_cpu_idle(void)
 {
-	if (!test_cpu_flag(CIF_MCCK_PENDING))
-		/* Halt the cpu and keep track of cpu time accounting. */
 	enabled_wait();
 	local_irq_enable();
 }
 
 void arch_cpu_idle_exit(void)
 {
-	local_mcck_enable();
-	if (test_cpu_flag(CIF_MCCK_PENDING))
-		s390_handle_mcck();
 }
 
 void arch_cpu_idle_dead(void)

arch/s390/kernel/nmi.c

@@ -148,7 +148,6 @@ void s390_handle_mcck(void)
 	local_mcck_disable();
 	mcck = *this_cpu_ptr(&cpu_mcck);
 	memset(this_cpu_ptr(&cpu_mcck), 0, sizeof(mcck));
-	clear_cpu_flag(CIF_MCCK_PENDING);
 	local_mcck_enable();
 	local_irq_restore(flags);
 
@@ -333,7 +332,7 @@ NOKPROBE_SYMBOL(s390_backup_mcck_info);
 /*
  * machine check handler.
  */
-void notrace s390_do_machine_check(struct pt_regs *regs)
+int notrace s390_do_machine_check(struct pt_regs *regs)
 {
 	static int ipd_count;
 	static DEFINE_SPINLOCK(ipd_lock);
@@ -342,6 +341,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 	unsigned long long tmp;
 	union mci mci;
 	unsigned long mcck_dam_code;
+	int mcck_pending = 0;
 
 	nmi_enter();
 	inc_irq_stat(NMI_NMI);
@@ -400,7 +400,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 		 */
 		mcck->kill_task = 1;
 		mcck->mcck_code = mci.val;
-		set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 
 	/*
@@ -420,8 +420,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 			mcck->stp_queue |= stp_sync_check();
 		if (S390_lowcore.external_damage_code & (1U << ED_STP_ISLAND))
 			mcck->stp_queue |= stp_island_check();
-		if (mcck->stp_queue)
-			set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 
 	/*
@@ -442,12 +441,12 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 	if (mci.cp) {
 		/* Channel report word pending */
 		mcck->channel_report = 1;
-		set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 	if (mci.w) {
 		/* Warning pending */
 		mcck->warning = 1;
-		set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 
 	/*
@@ -462,7 +461,17 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 		*((long *)(regs->gprs[15] + __SF_SIE_REASON)) = -EINTR;
 	}
 	clear_cpu_flag(CIF_MCCK_GUEST);
+
+	if (user_mode(regs) && mcck_pending) {
+		nmi_exit();
+		return 1;
+	}
+
+	if (mcck_pending)
+		schedule_mcck_handler();
+
 	nmi_exit();
+	return 0;
 }
 NOKPROBE_SYMBOL(s390_do_machine_check);
 

arch/s390/kernel/setup.c

@@ -384,8 +384,7 @@ static void __init setup_lowcore_dat_off(void)
 	lc->restart_psw.addr = (unsigned long) restart_int_handler;
 	lc->external_new_psw.mask = PSW_KERNEL_BITS | PSW_MASK_MCHECK;
 	lc->external_new_psw.addr = (unsigned long) ext_int_handler;
-	lc->svc_new_psw.mask = PSW_KERNEL_BITS |
-		PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK;
+	lc->svc_new_psw.mask = PSW_KERNEL_BITS | PSW_MASK_MCHECK;
 	lc->svc_new_psw.addr = (unsigned long) system_call;
 	lc->program_new_psw.mask = PSW_KERNEL_BITS | PSW_MASK_MCHECK;
 	lc->program_new_psw.addr = (unsigned long) pgm_check_handler;

arch/s390/kvm/kvm-s390.c

@@ -3995,9 +3995,6 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu)
 	if (need_resched())
 		schedule();
 
-	if (test_cpu_flag(CIF_MCCK_PENDING))
-		s390_handle_mcck();
-
 	if (!kvm_is_ucontrol(vcpu->kvm)) {
 		rc = kvm_s390_deliver_pending_interrupts(vcpu);
 		if (rc)

arch/s390/kvm/vsie.c

@@ -1002,8 +1002,6 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 
 	if (need_resched())
 		schedule();
-	if (test_cpu_flag(CIF_MCCK_PENDING))
-		s390_handle_mcck();
 
 	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
 

arch/s390/lib/delay.c

@@ -33,7 +33,7 @@ EXPORT_SYMBOL(__delay);
 
 static void __udelay_disabled(unsigned long long usecs)
 {
-	unsigned long cr0, cr0_new, psw_mask;
+	unsigned long cr0, cr0_new, psw_mask, flags;
 	struct s390_idle_data idle;
 	u64 end;
 
@@ -45,7 +45,9 @@ static void __udelay_disabled(unsigned long long usecs)
 	psw_mask = __extract_psw() | PSW_MASK_EXT | PSW_MASK_WAIT;
 	set_clock_comparator(end);
 	set_cpu_flag(CIF_IGNORE_IRQ);
+	local_irq_save(flags);
 	psw_idle(&idle, psw_mask);
+	local_irq_restore(flags);
 	clear_cpu_flag(CIF_IGNORE_IRQ);
 	set_clock_comparator(S390_lowcore.clock_comparator);
 	__ctl_load(cr0, 0, 0);