[PATCH v2] hmi: Move hmi irq stat from percpu variable to paca.

[Mahesh Salgaonkar]

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 hmi handler to 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/20200608070904.387440-1-aneesh.kumar@linux.ibm.com/

Suggested-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
Signed-off-by: Mahesh Salgaonkar <mahesh at linux.ibm.com>
---
Machine check handling as well touches percpu variables in realmode. Will
address that in separate patchset.

Change in v2:
- Fix the build failures for pmac32 and ppc64e configs.
---
 arch/powerpc/include/asm/hardirq.h |    1 -
 arch/powerpc/include/asm/paca.h    |    1 +
 arch/powerpc/kernel/irq.c          |    8 ++++++--
 arch/powerpc/kernel/mce.c          |    2 +-
 arch/powerpc/kvm/book3s_hv_ras.c   |    2 +-
 5 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/hardirq.h b/arch/powerpc/include/asm/hardirq.h
index f1e9067bd5ac..f133b5930ae1 100644
--- a/arch/powerpc/include/asm/hardirq.h
+++ b/arch/powerpc/include/asm/hardirq.h
@@ -13,7 +13,6 @@ typedef struct {
 	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;
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 45a839a7c6cf..cc07c399306e 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -225,6 +225,7 @@ struct paca_struct {
 	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 */
 
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 112d150354b2..a05f9ce05459 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -621,13 +621,15 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 		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);
+					paca_ptrs[j]->hmi_irqs);
 		seq_printf(p, "  Hypervisor Maintenance Interrupts\n");
 	}
+#endif
 
 	seq_printf(p, "%*s: ", prec, "NMI");
 	for_each_online_cpu(j)
@@ -665,7 +667,9 @@ u64 arch_irq_stat_cpu(unsigned int cpu)
 	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;
diff --git a/arch/powerpc/kernel/mce.c b/arch/powerpc/kernel/mce.c
index fd90c0eda229..dc11fc16750f 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -711,7 +711,7 @@ long hmi_exception_realmode(struct pt_regs *regs)
 {	
 	int ret;
 
-	__this_cpu_inc(irq_stat.hmi_exceptions);
+	local_paca->hmi_irqs++;
 
 	ret = hmi_handle_debugtrig(regs);
 	if (ret >= 0)
diff --git a/arch/powerpc/kvm/book3s_hv_ras.c b/arch/powerpc/kvm/book3s_hv_ras.c
index 79f7d07ef674..6028628ea3ac 100644
--- a/arch/powerpc/kvm/book3s_hv_ras.c
+++ b/arch/powerpc/kvm/book3s_hv_ras.c
@@ -244,7 +244,7 @@ long kvmppc_realmode_hmi_handler(void)
 {
 	bool resync_req;
 
-	__this_cpu_inc(irq_stat.hmi_exceptions);
+	local_paca->hmi_irqs++;
 
 	if (hmi_handle_debugtrig(NULL) >= 0)
 		return 1;