KVM: arm64: Disassociate vcpus from redistributor region on teardown

When tearing down a redistributor region, make sure we don't have
any dangling pointer to that region stored in a vcpu.

Fixes: e5a35635 ("kvm: arm64: vgic-v3: Introduce vgic_v3_free_redist_region()")
Reported-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240605175637.1635653-1-maz@kernel.org
Cc: stable@vger.kernel.org

arch/arm64/kvm/vgic/vgic-init.c

@@ -391,7 +391,7 @@ static void kvm_vgic_dist_destroy(struct kvm *kvm)
 
 	if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
 		list_for_each_entry_safe(rdreg, next, &dist->rd_regions, list)
-			vgic_v3_free_redist_region(rdreg);
+			vgic_v3_free_redist_region(kvm, rdreg);
 		INIT_LIST_HEAD(&dist->rd_regions);
 	} else {
 		dist->vgic_cpu_base = VGIC_ADDR_UNDEF;

arch/arm64/kvm/vgic/vgic-mmio-v3.c

@@ -919,8 +919,19 @@ static int vgic_v3_alloc_redist_region(struct kvm *kvm, uint32_t index,
 	return ret;
 }
 
-void vgic_v3_free_redist_region(struct vgic_redist_region *rdreg)
+void vgic_v3_free_redist_region(struct kvm *kvm, struct vgic_redist_region *rdreg)
 {
+	struct kvm_vcpu *vcpu;
+	unsigned long c;
+
+	lockdep_assert_held(&kvm->arch.config_lock);
+
+	/* Garbage collect the region */
+	kvm_for_each_vcpu(c, vcpu, kvm) {
+		if (vcpu->arch.vgic_cpu.rdreg == rdreg)
+			vcpu->arch.vgic_cpu.rdreg = NULL;
+	}
+
 	list_del(&rdreg->list);
 	kfree(rdreg);
 }
@@ -945,7 +956,7 @@ int vgic_v3_set_redist_base(struct kvm *kvm, u32 index, u64 addr, u32 count)
 
 		mutex_lock(&kvm->arch.config_lock);
 		rdreg = vgic_v3_rdist_region_from_index(kvm, index);
-		vgic_v3_free_redist_region(rdreg);
+		vgic_v3_free_redist_region(kvm, rdreg);
 		mutex_unlock(&kvm->arch.config_lock);
 		return ret;
 	}

arch/arm64/kvm/vgic/vgic.h

@@ -316,7 +316,7 @@ vgic_v3_rd_region_size(struct kvm *kvm, struct vgic_redist_region *rdreg)
 
 struct vgic_redist_region *vgic_v3_rdist_region_from_index(struct kvm *kvm,
 							   u32 index);
-void vgic_v3_free_redist_region(struct vgic_redist_region *rdreg);
+void vgic_v3_free_redist_region(struct kvm *kvm, struct vgic_redist_region *rdreg);
 
 bool vgic_v3_rdist_overlap(struct kvm *kvm, gpa_t base, size_t size);