Re: [PATCH 2/2] s390/vfio-ap: replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM notification

[Halil Pasic]

On Mon, 26 Jul 2021 19:03:17 -0300
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:

> > You may end up with open and close running interleaved. What I'
> > trying to say is, to my best knowledge, normally there is no
> > you have to close it before you open it again rule for files.  
> 
> This is an existing bug in this driver, I've fixed in the reflck series.
> 
> open_device/close_device will not run concurrently, or out of order,
> afer it is fixed.

Well if that is the case then provided your fix precedes this patch:

Acked-by: Halil Pasic <pasic@xxxxxxxxxxxxx>

I'm not entirely happy with this. I did not thoroughly investigate the
implications of reversing the locking order of the vfio-ap lock (driver
global) and the kvm lock (guest specific). I will trust Tony and hope
our KVM maintainers will scream if this is bad from interference and
delay perspective.

Regards,
Halil