powerpc/book3s: Print task info if we take a machine check in user mode

For an MCE (Machine Check Exception) that hits while in user mode
MSR(PR=1), print the task info to the console MCE error log. This may
help to identify an application that triggered the MCE.

After this patch the MCE console looks like:

Severe Machine check interrupt [Recovered]
NIP: [0000000010039778] PID: 762 Comm: ebizzy
Initiator: CPU
Error type: SLB [Multihit]
Effective address: 0000000010039778

Severe Machine check interrupt [Not recovered]
NIP: [0000000010039778] PID: 763 Comm: ebizzy
Initiator: CPU
Error type: UE [Page table walk ifetch]
Effective address: 0000000010039778
ebizzy[763]: unhandled signal 7 at 0000000010039778 nip 0000000010039778 lr 0000000010001b44 code 30004

Signed-off-by: Mahesh Salgaonkar <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/include/asm/mce.h

···
 extern int get_mce_event(struct machine_check_event *mce, bool release);
 extern void release_mce_event(void);
 extern void machine_check_queue_event(void);
-extern void machine_check_print_event_info(struct machine_check_event *evt);
+extern void machine_check_print_event_info(struct machine_check_event *evt,
+					   bool user_mode);
 extern uint64_t get_mce_fault_addr(struct machine_check_event *evt);
 
 #endif /* __ASM_PPC64_MCE_H__ */

arch/powerpc/kernel/mce.c

···
 	while (__this_cpu_read(mce_queue_count) > 0) {
 		index = __this_cpu_read(mce_queue_count) - 1;
 		machine_check_print_event_info(
-				this_cpu_ptr(&mce_event_queue[index]));
+				this_cpu_ptr(&mce_event_queue[index]), false);
 		__this_cpu_dec(mce_queue_count);
 	}
 }
 
-void machine_check_print_event_info(struct machine_check_event *evt)
+void machine_check_print_event_info(struct machine_check_event *evt,
+				    bool user_mode)
 {
 	const char *level, *sevstr, *subtype;
 	static const char *mc_ue_types[] = {
···
 	printk("%s%s Machine check interrupt [%s]\n", level, sevstr,
 	       evt->disposition == MCE_DISPOSITION_RECOVERED ?
 	       "Recovered" : "Not recovered");
-	printk("%s  NIP [%016llx]: %pS\n", level, evt->srr0, (void *)evt->srr0);
+
+	if (user_mode) {
+		printk("%s  NIP: [%016llx] PID: %d Comm: %s\n", level,
+			evt->srr0, current->pid, current->comm);
+	} else {
+		printk("%s  NIP [%016llx]: %pS\n", level, evt->srr0,
+		       (void *)evt->srr0);
+	}
+
 	printk("%s  Initiator: %s\n", level,
 	       evt->initiator == MCE_INITIATOR_CPU ? "CPU" : "Unknown");
 	switch (evt->error_type) {

arch/powerpc/platforms/powernv/opal.c

···
 		       evt.version);
 		return 0;
 	}
-	machine_check_print_event_info(&evt);
+	machine_check_print_event_info(&evt, user_mode(regs));
 
 	if (opal_recover_mce(regs, &evt))
 		return 1;