Re: [PATCH v17 14/15] s390/ap: notify drivers on config changed and scan complete callbacks

[Tony Krowiak]

On 2/7/22 20:38, Halil Pasic wrote:
> On Mon, 7 Feb 2022 14:39:31 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > > Back to the topic of locking: it looks to me that on this path you
> > > do the filtering and thus the accesses to matrix_mdev->shadow_apcb,
> > > matrix_mdev->matrix and matrix_dev->config_info some of which are
> > > of type write whithout the matrix_dev->lock held. More precisely
> > > only with the matrix_dev->guests_lock held in "read" mode.
> > >
> > > Did I misread the code? If not, how is that OK?
> > You make a valid point, a struct rw_semaphore is not adequate for the
> > purposes
> > it is used in this patch series. It needs to be a mutex.
> Good we agree that v17 is racy.
>
> > For v18 which is forthcoming probably this week, I've been reworking the
> > locking
> > based on your observation that the struct ap_guest is not necessary given we
> > already have a list of the mediated devices which contain the KVM
> > pointer. On the other
> [..]
> > > BTW I got delayed on my "locking rules" writeup. Sorry for that!
> > No worries, I've been writing up a vfio-ap-locking.rst document to
> > include with the next
> > version of the patch series.
> I'm looking forward to v18 including that document. I prefer not to
> discuss what you wrote about the approach taken in v18 now. It is easier
> to me when I have both the text stating the intended design, and the
> code that is supposed to adhere to this design.
>
> Regards,
> Halil

Coming soon to a theater near you:)

>