irqchip/gic: Take lock when updating irq type

Most MMIO GIC register accesses use a 1-hot bit scheme that
avoids requiring any form of locking. This isn't true for the
GICD_ICFGRn registers, which require a RMW sequence.

Unfortunately, we seem to be missing a lock for these particular
accesses, which could result in a race condition if changing the
trigger type on any two interrupts within the same set of 16
interrupts (and thus controlled by the same CFGR register).

Introduce a private lock in the GIC common comde for this
particular case, making it cover both GIC implementations
in one go.

Cc: stable@vger.kernel.org
Signed-off-by: Aniruddha Banerjee <aniruddhab@nvidia.com>
[maz: updated changelog]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/irq-gic-common.c

@@ -21,6 +21,8 @@
 
 #include "irq-gic-common.h"
 
+static DEFINE_RAW_SPINLOCK(irq_controller_lock);
+
 static const struct gic_kvm_info *gic_kvm_info;
 
 const struct gic_kvm_info *gic_get_kvm_info(void)
@@ -53,20 +55,24 @@ int gic_configure_irq(unsigned int irq, unsigned int type,
 	u32 confoff = (irq / 16) * 4;
 	u32 val, oldval;
 	int ret = 0;
+	unsigned long flags;
 
 	/*
 	 * Read current configuration register, and insert the config
 	 * for "irq", depending on "type".
 	 */
+	raw_spin_lock_irqsave(&irq_controller_lock, flags);
 	val = oldval = readl_relaxed(base + GIC_DIST_CONFIG + confoff);
 	if (type & IRQ_TYPE_LEVEL_MASK)
 		val &= ~confmask;
 	else if (type & IRQ_TYPE_EDGE_BOTH)
 		val |= confmask;
 
 	/* If the current configuration is the same, then we are done */
-	if (val == oldval)
+	if (val == oldval) {
+		raw_spin_unlock_irqrestore(&irq_controller_lock, flags);
 		return 0;
+	}
 
 	/*
 	 * Write back the new configuration, and possibly re-enable
@@ -84,6 +90,7 @@ int gic_configure_irq(unsigned int irq, unsigned int type,
 			pr_warn("GIC: PPI%d is secure or misconfigured\n",
 				irq - 16);
 	}
+	raw_spin_unlock_irqrestore(&irq_controller_lock, flags);
 
 	if (sync_access)
 		sync_access();