[PATCH v3 4/9] KVM: arm64: vgic: Let an interrupt controller advertise lack of HW deactivation

[Marc Zyngier]

The vGIC, as architected by ARM, allows a virtual interrupt to
trigger the deactivation of a physical interrupt. This allows
the following interrupt to be delivered without requiring an exit.

However, some implementations have choosen not to implement this,
meaning that we will need some unsavoury workarounds to deal with this.

On detecting such a case, taint the kernel and spit a nastygram.
We'll deal with this in later patches.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/vgic/vgic-init.c       | 10 ++++++++++
 include/kvm/arm_vgic.h                |  3 +++
 include/linux/irqchip/arm-vgic-info.h |  2 ++
 3 files changed, 15 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 9fd23f32aa54..5b06a9970a57 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -524,6 +524,16 @@ int kvm_vgic_hyp_init(void)
 	if (!gic_kvm_info)
 		return -ENODEV;
 
+	/*
+	 * If we get one of these oddball non-GICs, taint the kernel,
+	 * as we have no idea of how they *really* behave.
+	 */
+	if (gic_kvm_info->no_hw_deactivation) {
+		kvm_info("Non-architectural vgic, tainting kernel\n");
+		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+		kvm_vgic_global_state.no_hw_deactivation = true;
+	}
+
 	switch (gic_kvm_info->type) {
 	case GIC_V2:
 		ret = vgic_v2_probe(gic_kvm_info);
diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
index ec621180ef09..e45b26e8d479 100644
--- a/include/kvm/arm_vgic.h
+++ b/include/kvm/arm_vgic.h
@@ -72,6 +72,9 @@ struct vgic_global {
 	bool			has_gicv4;
 	bool			has_gicv4_1;
 
+	/* Pseudo GICv3 from outer space */
+	bool			no_hw_deactivation;
+
 	/* GIC system register CPU interface */
 	struct static_key_false gicv3_cpuif;
 
diff --git a/include/linux/irqchip/arm-vgic-info.h b/include/linux/irqchip/arm-vgic-info.h
index 0319636be928..d39d0b591c5a 100644
--- a/include/linux/irqchip/arm-vgic-info.h
+++ b/include/linux/irqchip/arm-vgic-info.h
@@ -30,6 +30,8 @@ struct gic_kvm_info {
 	bool		has_v4;
 	/* rvpeid support */
 	bool		has_v4_1;
+	/* Deactivation impared, subpar stuff */
+	bool		no_hw_deactivation;
 };
 
 #ifdef CONFIG_KVM
-- 
2.29.2