KVM: arm64: Use config_lock to protect vgic state

Almost all of the vgic state is VM-scoped but accessed from the context
of a vCPU. These accesses were serialized on the kvm->lock which cannot
be nested within a vcpu->mutex critical section.

Move over the vgic state to using the config_lock. Tweak the lock
ordering where necessary to ensure that the config_lock is acquired
after the vcpu->mutex. Acquire the config_lock in kvm_vgic_create() to
avoid a race between the converted flows and GIC creation. Where
necessary, continue to acquire kvm->lock to avoid a race with vCPU
creation (i.e. flows that use lock_all_vcpus()).

Finally, promote the locking expectations in comments to lockdep
assertions and update the locking documentation for the config_lock as
well as vcpu->mutex.

Cc: stable@vger.kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230327164747.2466958-5-oliver.upton@linux.dev

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/arm64/kvm/vgic/vgic-debug.c b/arch/arm64/kvm/vgic/vgic-debug.c
index 78cde687383c..07aa0437125a 100644
--- a/arch/arm64/kvm/vgic/vgic-debug.c
+++ b/arch/arm64/kvm/vgic/vgic-debug.c
@@ -85,7 +85,7 @@ static void *vgic_debug_start(struct seq_file *s, loff_t *pos)
 	struct kvm *kvm = s->private;
 	struct vgic_state_iter *iter;
 
-	mutex_lock(&kvm->lock);
+	mutex_lock(&kvm->arch.config_lock);
 	iter = kvm->arch.vgic.iter;
 	if (iter) {
 		iter = ERR_PTR(-EBUSY);
@@ -104,7 +104,7 @@ static void *vgic_debug_start(struct seq_file *s, loff_t *pos)
 	if (end_of_vgic(iter))
 		iter = NULL;
 out:
-	mutex_unlock(&kvm->lock);
+	mutex_unlock(&kvm->arch.config_lock);
 	return iter;
 }
 
@@ -132,12 +132,12 @@ static void vgic_debug_stop(struct seq_file *s, void *v)
 	if (IS_ERR(v))
 		return;
 
-	mutex_lock(&kvm->lock);
+	mutex_lock(&kvm->arch.config_lock);
 	iter = kvm->arch.vgic.iter;
 	kfree(iter->lpi_array);
 	kfree(iter);
 	kvm->arch.vgic.iter = NULL;
-	mutex_unlock(&kvm->lock);
+	mutex_unlock(&kvm->arch.config_lock);
 }
 
 static void print_dist_state(struct seq_file *s, struct vgic_dist *dist)