On 4/27/22 11:01 AM, Jason Gunthorpe wrote:
On Wed, Apr 27, 2022 at 10:42:07AM -0400, Matthew Rosato wrote:
On 4/27/22 10:04 AM, Jason Gunthorpe wrote:
On Tue, Apr 26, 2022 at 04:08:37PM -0400, Matthew Rosato wrote:
+static int vfio_pci_zdev_group_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct zpci_dev *zdev = container_of(nb, struct zpci_dev, nb);
+ int (*fn)(struct zpci_dev *zdev, struct kvm *kvm);
+ int rc = NOTIFY_OK;
+
+ if (action == VFIO_GROUP_NOTIFY_SET_KVM) {
+ if (!zdev)
+ return NOTIFY_DONE;
+
+ fn = symbol_get(kvm_s390_pci_register_kvm);
+ if (!fn)
+ return NOTIFY_DONE;
+
+ if (fn(zdev, (struct kvm *)data))
+ rc = NOTIFY_BAD;
+
+ symbol_put(kvm_s390_pci_register_kvm);
Is it possible this function can be in statically linked arch code?
Or, actually, is zPCI useful anyhow without kvm ie can you just have a
direct dependency here?
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.
Then if we find a usecase for a vfio-pci-zdev extension without KVM
later, we can further split vfio-pci-zdev and go back to building
vfio-pci-zdev when CONFIG_S390 but only build the kvm pieces (like the
code above) when you specify CONFIG_VFIO_PCI_ZDEV_KVM. This would
eliminate this symbol_get. Sound OK?
Or is there some technical blocker? (circular dep or something?)
Jason
