KVM: arm64: Enable GICv3 common sysreg trapping via command-line

Now that we're able to safely handle common sysreg access, let's
give the user the opportunity to enable it by passing a specific
command-line option (vgic_v3.common_trap).

Tested-by: Alexander Graf <agraf@suse.de>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -1837,6 +1837,10 @@
 			[KVM,ARM] Trap guest accesses to GICv3 group-1
 			system registers
 
+	kvm-arm.vgic_v3_common_trap=
+			[KVM,ARM] Trap guest accesses to GICv3 common
+			system registers
+
 	kvm-intel.ept=	[KVM,Intel] Disable extended page tables
 			(virtualized MMU) support on capable Intel chips.
 			Default is 1 (enabled)

include/linux/irqchip/arm-gic-v3.h

@@ -417,6 +417,7 @@
 
 #define ICH_HCR_EN			(1 << 0)
 #define ICH_HCR_UIE			(1 << 1)
+#define ICH_HCR_TC			(1 << 10)
 #define ICH_HCR_TALL0			(1 << 11)
 #define ICH_HCR_TALL1			(1 << 12)
 #define ICH_HCR_EOIcount_SHIFT		27

virt/kvm/arm/vgic/vgic-v3.c

@@ -23,6 +23,7 @@
 
 static bool group0_trap;
 static bool group1_trap;
+static bool common_trap;
 
 void vgic_v3_set_underflow(struct kvm_vcpu *vcpu)
 {
@@ -265,6 +266,8 @@ void vgic_v3_enable(struct kvm_vcpu *vcpu)
 		vgic_v3->vgic_hcr |= ICH_HCR_TALL0;
 	if (group1_trap)
 		vgic_v3->vgic_hcr |= ICH_HCR_TALL1;
+	if (common_trap)
+		vgic_v3->vgic_hcr |= ICH_HCR_TC;
 }
 
 int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq)
@@ -450,6 +453,12 @@ static int __init early_group1_trap_cfg(char *buf)
 }
 early_param("kvm-arm.vgic_v3_group1_trap", early_group1_trap_cfg);
 
+static int __init early_common_trap_cfg(char *buf)
+{
+	return strtobool(buf, &common_trap);
+}
+early_param("kvm-arm.vgic_v3_common_trap", early_common_trap_cfg);
+
 /**
  * vgic_v3_probe - probe for a GICv3 compatible interrupt controller in DT
  * @node:	pointer to the DT node
@@ -508,7 +517,7 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
 	}
 #endif
 
-	if (group0_trap || group1_trap) {
+	if (group0_trap || group1_trap || common_trap) {
 		kvm_info("GICv3 sysreg trapping enabled (reduced performance)\n");
 		static_branch_enable(&vgic_v3_cpuif_trap);
 	}