Re: [PATCH 0/4] KVM: PPC: Book3S: Fix potential deadlocks

[Paul Mackerras <paulus@ozlabs.org>]

On Thu, May 23, 2019 at 05:21:00PM +1000, Alexey Kardashevskiy wrote:
> 
> 
> On 23/05/2019 16:34, Paul Mackerras wrote:
> > Recent reports of lockdep splats in the HV KVM code revealed that it
> > was taking the kvm->lock mutex in several contexts where a vcpu mutex
> > was already held.  Lockdep has only started warning since I added code
> > to take the vcpu mutexes in the XIVE device release functions, but
> > since Documentation/virtual/kvm/locking.txt specifies that the vcpu
> > mutexes nest inside kvm->lock, it seems that the new code is correct
> > and it is most of the old uses of kvm->lock that are wrong.
> > 
> > This series should fix the problems, by adding new mutexes that nest
> > inside the vcpu mutexes and using them instead of kvm->lock.
> 
> 
> I applied these 4, compiled, installed, rebooted, tried running a guest
> (which failed because I also updated QEMU and its cli has changed), got
> this. So VM was created and then destroyed without executing a single
> instruction, if that matters.

Looks like I need to remove the
	lockdep_assert_held(&kvm->arch.rtas_token_lock);

in kvmppc_rtas_tokens_free().  We don't have the rtas_token_lock, but
it doesn't matter because we are destroying the VM and nothing else
has a reference to it by now.

Paul.