KVM: arm/arm64: Fix GICv4 ITS initialization issues

We should only try to initialize GICv4 data structures on a GICv4
capable system.  Move the vgic_supports_direct_msis() check inito
vgic_v4_init() so that any KVM VGIC initialization path does not fail
on non-GICv4 systems.

Also be slightly more strict in the checking of the return value in
vgic_its_create, and only error out on negative return values from the
vgic_v4_init() function.  This is important because the kvm device code
only treats negative values as errors and only cleans up in this case.
Errornously treating a positive return value as an error from the
vgic_v4_init() function can lead to NULL pointer dereferences, as has
recently been observed.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

3 files changed, 7 insertions, 6 deletions

diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
index 40be908da238..62310122ee78 100644
--- a/virt/kvm/arm/vgic/vgic-init.c
+++ b/virt/kvm/arm/vgic/vgic-init.c
@@ -285,11 +285,9 @@ int vgic_init(struct kvm *kvm)
         if (ret)
                 goto out;
 
-        if (vgic_supports_direct_msis(kvm)) {
-                ret = vgic_v4_init(kvm);
-                if (ret)
-                        goto out;
-        }
+        ret = vgic_v4_init(kvm);
+        if (ret)
+                goto out;
 
         kvm_for_each_vcpu(i, vcpu, kvm)
                 kvm_vgic_vcpu_enable(vcpu);
diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index b8c1b724ba3e..c93ecd4a903b 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -1673,7 +1673,7 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
 
         if (vgic_initialized(dev->kvm)) {
                 int ret = vgic_v4_init(dev->kvm);
-                if (ret) {
+                if (ret < 0) {
                         kfree(its);
                         return ret;
                 }
diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
index 915d09dc2638..53c324aa44ef 100644
--- a/virt/kvm/arm/vgic/vgic-v4.c
+++ b/virt/kvm/arm/vgic/vgic-v4.c
@@ -118,6 +118,9 @@ int vgic_v4_init(struct kvm *kvm)
         struct kvm_vcpu *vcpu;
         int i, nr_vcpus, ret;
 
+        if (!vgic_supports_direct_msis(kvm))
+                return 0; /* Nothing to see here... move along. */
+
         if (dist->its_vm.vpes)
                 return 0;