KVM: arm64: vgic: Don't acquire its_lock before config_lock

commit f00327731131 ("KVM: arm64: Use config_lock to protect vgic
state") was meant to rectify a longstanding lock ordering issue in KVM
where the kvm->lock is taken while holding vcpu->mutex. As it so
happens, the aforementioned commit introduced yet another locking issue
by acquiring the its_lock before acquiring the config lock.

This is obviously wrong, especially considering that the lock ordering
is well documented in vgic.c. Reshuffle the locks once more to take the
config_lock before the its_lock. While at it, sprinkle in the lockdep
hinting that has become popular as of late to keep lockdep apprised of
our ordering.

Cc: stable@vger.kernel.org
Fixes: f00327731131 ("KVM: arm64: Use config_lock to protect vgic state")
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230412062733.988229-1-oliver.upton@linux.dev

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index 7713cd0..750e51e 100644 (file)
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -1958,6 +1958,16 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
        mutex_init(&its->its_lock);
        mutex_init(&its->cmd_lock);
 
+       /* Yep, even more trickery for lock ordering... */
+#ifdef CONFIG_LOCKDEP
+       mutex_lock(&dev->kvm->arch.config_lock);
+       mutex_lock(&its->cmd_lock);
+       mutex_lock(&its->its_lock);
+       mutex_unlock(&its->its_lock);
+       mutex_unlock(&its->cmd_lock);
+       mutex_unlock(&dev->kvm->arch.config_lock);
+#endif
+
        its->vgic_its_base = VGIC_ADDR_UNDEF;
 
        INIT_LIST_HEAD(&its->device_list);
@@ -2752,15 +2762,14 @@ static int vgic_its_ctrl(struct kvm *kvm, struct vgic_its *its, u64 attr)
                return 0;
 
        mutex_lock(&kvm->lock);
-       mutex_lock(&its->its_lock);
 
        if (!lock_all_vcpus(kvm)) {
-               mutex_unlock(&its->its_lock);
                mutex_unlock(&kvm->lock);
                return -EBUSY;
        }
 
        mutex_lock(&kvm->arch.config_lock);
+       mutex_lock(&its->its_lock);
 
        switch (attr) {
        case KVM_DEV_ARM_ITS_CTRL_RESET:
@@ -2774,9 +2783,9 @@ static int vgic_its_ctrl(struct kvm *kvm, struct vgic_its *its, u64 attr)
                break;
        }
 
+       mutex_unlock(&its->its_lock);
        mutex_unlock(&kvm->arch.config_lock);
        unlock_all_vcpus(kvm);
-       mutex_unlock(&its->its_lock);
        mutex_unlock(&kvm->lock);
        return ret;
 }