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/20200608070904.387440-1-aneesh.kumar@linux.ibm.com/

Suggested-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/159290806973.3642154.5244613424529764050.stgit@jupiter

5 files changed, 9 insertions, 6 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 05b1cc0e009e..bf21ebd36190 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -621,13 +621,14 @@ 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);
+			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)
@@ -665,7 +666,9 @@ 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 c2fa8ee63720..ada59f6c4298 100644
--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -727,7 +727,7 @@ 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;