[RFC v3 3/9] irqchip: gic: Provide support for interrupt grouping

[Daniel Thompson]

All GIC hardware except GICv1 without TrustZone support provides a means
to group exceptions into group 0 (which can optionally be signally using
use FIQ) and group 1. The kernel currently provides no means to exploit
this. This patch alters the initialization of the GIC to place all
interrupts into group 1, this is a foundational requirement to meaningfully
use FIQ.

Note that the hardware functionality is unavailable to the kernel when a
secure monitor is present because access to the grouping registers are
prohibited outside "secure world". This allows grouping to be used to
allow hardware peripherals to send interrupts into the secure world.

On systems without TrustZone support the kernel has the power to
route interrupt sources to FIQ, potentially allowing a driver to exploit the
NMI-like properties of FIQ.

The registers involved are RAZ/WI when unimplemented or protected by
security policy. This patch therefore applies grouping unconditionally.

Tested on a qemu GICv2 model (self-written from GICv2 spec) and
an STiH416 (ARM Cortex A9, GICv1, TZ).

Signed-off-by: Daniel Thompson <daniel.thompson at linaro.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Jason Cooper <jason at lakedaemon.net>
Cc: Nicolas Pitre <nicolas.pitre at linaro.org>
Cc: Christoffer Dall <christoffer.dall at linaro.org>
Cc: Sricharan R <r.sricharan at ti.com>
Acked-by: Dirk Behme <dirk.behme at de.bosch.com>
---
 drivers/irqchip/irq-gic.c       | 35 ++++++++++++++++++++++++++++++-----
 include/linux/irqchip/arm-gic.h |  3 +++
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index 57d165e..aa8efe4 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -408,13 +408,27 @@ static void __init gic_dist_init(struct gic_chip_data *gic)
 		writel_relaxed(0xa0a0a0a0, base + GIC_DIST_PRI + i * 4 / 4);
 
 	/*
+	 * Set all global interrupts to be group 1.
+	 *
+	 * If grouping is not available (not implemented or prohibited by
+	 * security mode) these registers a read-as-zero/write-ignored.
+	 */
+	for (i = 32; i < gic_irqs; i += 32)
+		writel_relaxed(0xffffffff, base + GIC_DIST_IGROUP + i * 4 / 32);
+
+	/*
 	 * Disable all interrupts.  Leave the PPI and SGIs alone
 	 * as these enables are banked registers.
 	 */
 	for (i = 32; i < gic_irqs; i += 32)
 		writel_relaxed(0xffffffff, base + GIC_DIST_ENABLE_CLEAR + i * 4 / 32);
 
-	writel_relaxed(1, base + GIC_DIST_CTRL);
+	/*
+	 * Set EnableGrp1/EnableGrp0 (bit 1 and 0) or EnableGrp (bit 0 only,
+	 * bit 1 ignored)
+	 */
+	writel_relaxed(GIC_DIST_CTRL_ENABLE_GRP0_BIT |
+		       GIC_DIST_CTRL_ENABLE_GRP1_BIT, base + GIC_DIST_CTRL);
 }
 
 static void gic_cpu_init(struct gic_chip_data *gic)
@@ -452,8 +466,16 @@ static void gic_cpu_init(struct gic_chip_data *gic)
 	for (i = 0; i < 32; i += 4)
 		writel_relaxed(0xa0a0a0a0, dist_base + GIC_DIST_PRI + i * 4 / 4);
 
+	/*
+	 * Set all PPI and SGI interrupts to be group 1.
+	 *
+	 * If grouping is not available (not implemented or prohibited by
+	 * security mode) these registers are read-as-zero/write-ignored.
+	 */
+	writel_relaxed(0xffffffff, dist_base + GIC_DIST_IGROUP + 0);
+
 	writel_relaxed(0xf0, base + GIC_CPU_PRIMASK);
-	writel_relaxed(1, base + GIC_CPU_CTRL);
+	writel_relaxed(0x1f, base + GIC_CPU_CTRL);
 }
 
 void gic_cpu_if_down(void)
@@ -537,7 +559,9 @@ static void gic_dist_restore(unsigned int gic_nr)
 		writel_relaxed(gic_data[gic_nr].saved_spi_enable[i],
 			dist_base + GIC_DIST_ENABLE_SET + i * 4);
 
-	writel_relaxed(1, dist_base + GIC_DIST_CTRL);
+	writel_relaxed(GIC_DIST_CTRL_ENABLE_GRP0_BIT |
+			   GIC_DIST_CTRL_ENABLE_GRP1_BIT,
+		       dist_base + GIC_DIST_CTRL);
 }
 
 static void gic_cpu_save(unsigned int gic_nr)
@@ -594,7 +618,7 @@ static void gic_cpu_restore(unsigned int gic_nr)
 		writel_relaxed(0xa0a0a0a0, dist_base + GIC_DIST_PRI + i * 4);
 
 	writel_relaxed(0xf0, cpu_base + GIC_CPU_PRIMASK);
-	writel_relaxed(1, cpu_base + GIC_CPU_CTRL);
+	writel_relaxed(0x1f, cpu_base + GIC_CPU_CTRL);
 }
 
 static int gic_notifier(struct notifier_block *self, unsigned long cmd,	void *v)
@@ -670,7 +694,8 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
 	dmb(ishst);
 
 	/* this always happens on GIC0 */
-	writel_relaxed(map << 16 | irq, gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
+	writel_relaxed(map << 16 | irq | 0x8000,
+		       gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT);
 
 	raw_spin_unlock_irqrestore(&irq_controller_lock, flags);
 }
diff --git a/include/linux/irqchip/arm-gic.h b/include/linux/irqchip/arm-gic.h
index 7ed92d0..919502f 100644
--- a/include/linux/irqchip/arm-gic.h
+++ b/include/linux/irqchip/arm-gic.h
@@ -37,6 +37,9 @@
 #define GIC_DIST_SGI_PENDING_CLEAR	0xf10
 #define GIC_DIST_SGI_PENDING_SET	0xf20
 
+#define GIC_DIST_CTRL_ENABLE_GRP0_BIT	(1 << 0)
+#define GIC_DIST_CTRL_ENABLE_GRP1_BIT	(1 << 1)
+
 #define GICH_HCR			0x0
 #define GICH_VTR			0x4
 #define GICH_VMCR			0x8
-- 
1.9.0