[PATCH 2/2] irqchip/gic-v3-its: Disable vSGI upon (CPUIF < v4.1) detection

[Lorenzo Pieralisi]

GIC CPU interfaces versions predating GIC v4.1 were not built to
accommodate vINTID within the vSGI range; as reported in the GIC
specifications (8.2 "Changes to the CPU interface"), it is
CONSTRAINED UNPREDICTABLE to deliver a vSGI to a PE with
ID_AA64PFR0_EL1.GIC == b0001.

Check the GIC CPUIF version through the arm64 capabilities
infrastructure and disable vSGIs if a CPUIF version < 4.1 is
detected to prevent using vSGIs on systems where they may
misbehave.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
---
 drivers/irqchip/irq-gic-v3-its.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 0fec31931e11..6ed4ba60ba7e 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -39,6 +39,20 @@
 
 #include "irq-gic-common.h"
 
+#ifdef CONFIG_ARM64
+#include <asm/cpufeature.h>
+
+static inline bool gic_cpuif_has_vsgi(void)
+{
+	return cpus_have_const_cap(ARM64_HAS_GIC_CPUIF_VSGI);
+}
+#else
+static inline bool gic_cpuif_has_vsgi(void)
+{
+	return false;
+}
+#endif
+
 #define ITS_FLAGS_CMDQ_NEEDS_FLUSHING		(1ULL << 0)
 #define ITS_FLAGS_WORKAROUND_CAVIUM_22375	(1ULL << 1)
 #define ITS_FLAGS_WORKAROUND_CAVIUM_23144	(1ULL << 2)
@@ -5415,7 +5429,11 @@ int __init its_init(struct fwnode_handle *handle, struct rdists *rdists,
 	if (has_v4 & rdists->has_vlpis) {
 		const struct irq_domain_ops *sgi_ops;
 
-		if (has_v4_1)
+		/*
+		 * Enable vSGIs only if the ITS and the
+		 * GIC CPUIF support them.
+		 */
+		if (has_v4_1 && gic_cpuif_has_vsgi())
 			sgi_ops = &its_sgi_domain_ops;
 		else
 			sgi_ops = NULL;
-- 
2.29.1