Re: [PATCH] KVM: arm64: vgic: Fix soft lockup during VM teardown

Shanker Donthineni
2023-01-21T15:29:02Z

On 1/20/23 06:00, Marc Zyngier wrote:
> What I am asking agin is: is there any overlap between any vgic ioctl
> and the teardown of the VM? Do you ever see kvm_vm_release() being
> called before kvm_device_release()?
>
> Because that's the overlap I've been talking all along.

I've not observed overlap of kvm_vm_release() with ioctls kvm_device_ioctl(),
kvm_vcpu_ioctl() and kvm_vm_ioctl() for 3hrs. Test created hundreds of VMs and
teardowns.

Debug code:
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4f26b244f6d0..9c8409a894f5 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -800,7 +800,7 @@ struct kvm {
bool dirty_ring_with_bitmap;
bool vm_bugged;
bool vm_dead;
-
+ atomic_t checkoverlap;
#ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
struct notifier_block pm_notifier;
#endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9c60384b5ae0..a5a9071aeb19 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1370,9 +1370,13 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
{
struct kvm *kvm = filp->private_data;

+ atomic_inc(&kvm->checkoverlap);
+ pr_err("%s(%d) start kvm=%px\n",__func__,__LINE__, kvm);
+
kvm_irqfd_release(kvm);

kvm_put_kvm(kvm);
+ pr_err("%s(%d) end kvm=%px\n",__func__,__LINE__, kvm);
return 0;
}

@@ -4073,6 +4077,8 @@ static long kvm_vcpu_ioctl(struct file *filp,
if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
return -EINVAL;

+if (atomic_read(&vcpu->kvm->checkoverlap)) pr_err("%s(%d) overlap kvm=%px\n", __func__, __LINE__, vcpu->kvm);
+
/*
* Some architectures have vcpu ioctls that are asynchronous to vcpu
* execution; mutex_lock() would break them.
@@ -4346,6 +4352,8 @@ static long kvm_device_ioctl(struct file *filp, unsigned int ioctl,
if (dev->kvm->mm != current->mm || dev->kvm->vm_dead)
return -EIO;

+ if (atomic_read(&dev->kvm->checkoverlap)) pr_err("%s(%d) overlap kvm=%px\n", __func__, __LINE__, dev->kvm);
+
switch (ioctl) {
case KVM_SET_DEVICE_ATTR:
return kvm_device_ioctl_attr(dev, dev->ops->set_attr, arg);
@@ -4731,6 +4739,8 @@ static long kvm_vm_ioctl(struct file *filp,

if (kvm->mm != current->mm || kvm->vm_dead)
return -EIO;
+if (atomic_read(&kvm->checkoverlap)) pr_err("%s(%d) overlap kvm=%px\n", __func__, __LINE__, kvm);
+
switch (ioctl) {
case KVM_CREATE_VCPU:
r = kvm_vm_ioctl_create_vcpu(kvm, arg);