Re: [PATCH v6 16/21] vfio-pci/zdev: add open/close device hooks

[Christian Borntraeger]

Am 27.04.22 um 17:39 schrieb Jason Gunthorpe:
> On Wed, Apr 27, 2022 at 11:26:40AM -0400, Matthew Rosato wrote:
> > > > zPCI devices (zpci_dev) exist regardless of whether kvm is configured or
> > > > not, and you can e.g. bind the associated PCI device to vfio-pci when KVM is
> > > > not configured (or module not loaded) and get the existing vfio-pci-zdev
> > > > extensions for that device (extra VFIO_DEVICE_INFO response data).  Making a
> > > > direct dependency on KVM would remove that; this was discussed in a prior
> > > > version because this extra info is not used today outside of a KVM usecase
> > > > are not specific to kvm that need vfio-pci-zdev).
> > >
> > > I'm a bit confused, what is the drawback of just having a direct
> > > symbol dependency here? It means vfio loads a little extra kernel
> > > module code, but is that really a big worry given almost all vfio
> > > users on s390 will be using it with kvm?
> >
> > It's about trying to avoid loading unnecessary code (or at least giving a
> > way to turn it off).
> >
> > Previously I did something like....
> >
> > https://lore.kernel.org/kvm/20220204211536.321475-15-mjrosato@xxxxxxxxxxxxx/
> >
> > And could do so again; as discussed in the thread there, I can use e.g.
> > CONFIG_VFIO_PCI_ZDEV_KVM and make vfio-pci-zdev depend on KVM in this
> > series.  You only get the vfio-pci-zdev extensions when you configure KVM.
>
> That make sense to me, I'd rather see that then the symbol_get/put here

I agree with Jason here.