arm64: Switch to PMR masking when starting CPUs

Once the boot CPU has been prepared or a new secondary CPU has been
brought up, use ICC_PMR_EL1 to mask interrupts on that CPU and clear
PSR.I bit.

Since ICC_PMR_EL1 is initialized at CPU bringup, avoid overwriting
it in the GICv3 driver.
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Suggested-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/smp.c

@@ -35,6 +35,7 @@
 #include <linux/smp.h>
 #include <linux/seq_file.h>
 #include <linux/irq.h>
+#include <linux/irqchip/arm-gic-v3.h>
 #include <linux/percpu.h>
 #include <linux/clockchips.h>
 #include <linux/completion.h>
@@ -180,6 +181,24 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	return ret;
 }
 
+static void init_gic_priority_masking(void)
+{
+	u32 cpuflags;
+
+	if (WARN_ON(!gic_enable_sre()))
+		return;
+
+	cpuflags = read_sysreg(daif);
+
+	WARN_ON(!(cpuflags & PSR_I_BIT));
+
+	gic_write_pmr(GIC_PRIO_IRQOFF);
+
+	/* We can only unmask PSR.I if we can take aborts */
+	if (!(cpuflags & PSR_A_BIT))
+		write_sysreg(cpuflags & ~PSR_I_BIT, daif);
+}
+
 /*
  * This is the secondary CPU boot entry.  We're using this CPUs
  * idle thread stack, but a set of temporary page tables.
@@ -206,6 +225,9 @@ asmlinkage notrace void secondary_start_kernel(void)
 	 */
 	cpu_uninstall_idmap();
 
+	if (system_uses_irq_prio_masking())
+		init_gic_priority_masking();
+
 	preempt_disable();
 	trace_hardirqs_off();
 
@@ -426,6 +448,10 @@ void __init smp_prepare_boot_cpu(void)
 	 * and/or scheduling is enabled.
 	 */
 	apply_boot_alternatives();
+
+	/* Conditionally switch to GIC PMR for interrupt masking */
+	if (system_uses_irq_prio_masking())
+		init_gic_priority_masking();
 }
 
 static u64 __init of_get_cpu_mpidr(struct device_node *dn)

drivers/irqchip/irq-gic-v3.c

@@ -415,6 +415,9 @@ static u32 gic_get_pribits(void)
 static bool gic_has_group0(void)
 {
 	u32 val;
+	u32 old_pmr;
+
+	old_pmr = gic_read_pmr();
 
 	/*
 	 * Let's find out if Group0 is under control of EL3 or not by
@@ -430,6 +433,8 @@ static bool gic_has_group0(void)
 	gic_write_pmr(BIT(8 - gic_get_pribits()));
 	val = gic_read_pmr();
 
+	gic_write_pmr(old_pmr);
+
 	return val != 0;
 }
 
@@ -591,7 +596,8 @@ static void gic_cpu_sys_reg_init(void)
 	group0 = gic_has_group0();
 
 	/* Set priority mask register */
-	write_gicreg(DEFAULT_PMR_VALUE, ICC_PMR_EL1);
+	if (!gic_prio_masking_enabled())
+		write_gicreg(DEFAULT_PMR_VALUE, ICC_PMR_EL1);
 
 	/*
 	 * Some firmwares hand over to the kernel with the BPR changed from