powerpc/64s: Move HMI IRQ stat from percpu variable to paca.

With the proposed change in percpu bootmem allocator to use page
mapping [1], the percpu first chunk memory area can come from vmalloc
ranges. This makes the HMI (Hypervisor Maintenance Interrupt) handler
crash the kernel whenever percpu variable is accessed in real mode.
This patch fixes this issue by moving the HMI IRQ stat inside paca for
safe access in realmode.

[1] https://lore.kernel.org/linuxppc-dev/[e-mail]/

Suggested-by: Aneesh Kumar K.V <[e-mail]>
Signed-off-by: Mahesh Salgaonkar <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/159290806973.3642154.5244613424529764050.stgit@jupiter

arch/powerpc/include/asm/hardirq.h

···
 	unsigned int pmu_irqs;
 	unsigned int mce_exceptions;
 	unsigned int spurious_irqs;
-	unsigned int hmi_exceptions;
 	unsigned int sreset_irqs;
 #ifdef CONFIG_PPC_WATCHDOG
 	unsigned int soft_nmi_irqs;

arch/powerpc/include/asm/paca.h

···
 	u16 in_mce;
 	u8 hmi_event_available;		/* HMI event is available */
 	u8 hmi_p9_special_emu;		/* HMI P9 special emulation */
+	u32 hmi_irqs;			/* HMI irq stat */
 #endif
 	u8 ftrace_enabled;		/* Hard disable ftrace */
 

arch/powerpc/kernel/irq.c

···
 		seq_printf(p, "%10u ", per_cpu(irq_stat, j).mce_exceptions);
 	seq_printf(p, "  Machine check exceptions\n");
 
+#ifdef CONFIG_PPC_BOOK3S_64
 	if (cpu_has_feature(CPU_FTR_HVMODE)) {
 		seq_printf(p, "%*s: ", prec, "HMI");
 		for_each_online_cpu(j)
-			seq_printf(p, "%10u ",
-					per_cpu(irq_stat, j).hmi_exceptions);
+			seq_printf(p, "%10u ", paca_ptrs[j]->hmi_irqs);
 		seq_printf(p, "  Hypervisor Maintenance Interrupts\n");
 	}
+#endif
 
 	seq_printf(p, "%*s: ", prec, "NMI");
 	for_each_online_cpu(j)
···
 	sum += per_cpu(irq_stat, cpu).mce_exceptions;
 	sum += per_cpu(irq_stat, cpu).spurious_irqs;
 	sum += per_cpu(irq_stat, cpu).timer_irqs_others;
-	sum += per_cpu(irq_stat, cpu).hmi_exceptions;
+#ifdef CONFIG_PPC_BOOK3S_64
+	sum += paca_ptrs[cpu]->hmi_irqs;
+#endif
 	sum += per_cpu(irq_stat, cpu).sreset_irqs;
 #ifdef CONFIG_PPC_WATCHDOG
 	sum += per_cpu(irq_stat, cpu).soft_nmi_irqs;

arch/powerpc/kernel/mce.c

···
 {	
 	int ret;
 
-	__this_cpu_inc(irq_stat.hmi_exceptions);
+	local_paca->hmi_irqs++;
 
 	ret = hmi_handle_debugtrig(regs);
 	if (ret >= 0)

arch/powerpc/kvm/book3s_hv_ras.c

···
 {
 	bool resync_req;
 
-	__this_cpu_inc(irq_stat.hmi_exceptions);
+	local_paca->hmi_irqs++;
 
 	if (hmi_handle_debugtrig(NULL) >= 0)
 		return 1;