Re: [PATCH] kvm/vfio: Fix potential deadlock on vfio group_lock

[Matthew Rosato]

On 1/31/23 9:48 AM, Jason Gunthorpe wrote:
> On Tue, Jan 31, 2023 at 09:46:18AM -0500, Anthony Krowiak wrote:
> 
>>> Maybe you should split that lock and have a dedicated apcb lock?
>>
>> I don't think that would suffice for taking the vCPUs out of SIE.
> 
> Then I think we have to keep this patch and also do Matthew's patch to
> keep kvm refs inside vfio as well.
> 

I don't think keeping kvm refs inside vfio solves this issue though -- Even if we handle the kvm_put_kvm asynchronously within vfio as previously proposed, kvm_vfio_release will eventually get called and it gets called with the kvm->lock already held, then proceeds to call vfio_file_set_kvm which gets the group->lock.  That order conflicts with the hierarchy used by the driver during open_device of vfio->group_lock ... kvm->lock.