s390/cpum_cf: introduce kernel_cpumcf_alert() to obtain measurement alerts

During a __kernel_cpumcf_begin()/end() session, save measurement alerts
for the counter facility in the per-CPU cpu_cf_events variable.
Users can obtain and, optionally, clear the alerts by calling
kernel_cpumcf_alert() to specifically handle alerts.

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

arch/s390/include/asm/cpu_mcf.h

···
 struct cpu_cf_events {
 	struct cpumf_ctr_info	info;
 	atomic_t		ctr_set[CPUMF_CTR_SET_MAX];
+	atomic64_t		alert;
 	u64			state, tx_state;
 	unsigned int		flags;
 	unsigned int		txn_flags;
···
 DECLARE_PER_CPU(struct cpu_cf_events, cpu_cf_events);
 
 int __kernel_cpumcf_begin(void);
+unsigned long kernel_cpumcf_alert(int clear);
 void __kernel_cpumcf_end(void);
 
 #endif /* _ASM_S390_CPU_MCF_H */

arch/s390/kernel/perf_cpum_cf.c

···
 		[CPUMF_CTR_SET_EXT]	= ATOMIC_INIT(0),
 		[CPUMF_CTR_SET_MT_DIAG] = ATOMIC_INIT(0),
 	},
+	.alert = ATOMIC64_INIT(0),
 	.state = 0,
 	.flags = 0,
 	.txn_flags = 0,
···
 	if (alert & CPU_MF_INT_CF_MTDA)
 		pr_warn("CPU[%i] MT counter data was lost\n",
 			smp_processor_id());
+
+	/* store alert for special handling by in-kernel users */
+	atomic64_or(alert, &cpuhw->alert);
 }
 
 #define PMC_INIT      0
···
 	return 0;
 }
 EXPORT_SYMBOL(__kernel_cpumcf_begin);
+
+/* Obtain the CPU-measurement alerts for the counter facility */
+unsigned long kernel_cpumcf_alert(int clear)
+{
+	struct cpu_cf_events *cpuhw = this_cpu_ptr(&cpu_cf_events);
+	unsigned long alert;
+
+	alert = atomic64_read(&cpuhw->alert);
+	if (clear)
+		atomic64_set(&cpuhw->alert, 0);
+
+	return alert;
+}
+EXPORT_SYMBOL(kernel_cpumcf_alert);
 
 /* Release the CPU-measurement counter facility */
 void __kernel_cpumcf_end(void)