On Tue, Apr 23, 2019 at 04:42:28PM -0600, Alex Williamson wrote: > The PCIe bandwidth notification service generates logging any time a > link changes speed or width to a state that is considered downgraded. > Unfortunately, it cannot differentiate signal integrity related link > changes from those intentionally initiated by an endpoint driver, > including drivers that may live in userspace or VMs when making use > of vfio-pci. Therefore, allow the driver to have a say in whether > the link is indeed downgraded and worth noting in the log, or if the > change is perhaps intentional. > > For vfio-pci, we don't know the intentions of the user/guest driver > either, but we do know that GPU drivers in guests actively manage > the link state and therefore trigger the bandwidth notification for > what appear to be entirely intentional link changes. > > Fixes: e8303bb7a75c PCI/LINK: Report degraded links via link bandwidth notification > Link: https://lore.kernel.org/linux-pci/155597243666.19387.1205950870601742062.stgit@xxxxxxxxxx/T/#u > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > --- > > Changing to pci_dbg() logging is not super usable, so let's try the > previous idea of letting the driver handle link change events as they > see fit. Ideally this might be two patches, but for easier handling, > folding the pci and vfio-pci bits together. Comments? Thanks, I'm a little uneasy about the bandwidth notification logging as a whole. Messages in dmesg don't seem like a solid base for building management tools. I assume the eventual goal would be some sort of digested notification along the lines of "hey mr/ms administrator, the link to device X unexpectedly became slower, you might want to check that out." If I were building that, I don't think I would use dmesg. I might write a daemon that polls /sys/.../current_link_{speed,width}, or maybe use some sort of netlink event. Maybe it would be useful to have the admin designate devices of interest. I'm hesitant about adding a .link_change() handler. If there's something useful a driver could do with it, that's one thing. But using it merely to suppress a message doesn't really seem worth the trouble, and it seems unfriendly to ask drivers to add it when they didn't ask for it and get no benefit from it. > drivers/pci/probe.c | 13 +++++++++++++ > drivers/vfio/pci/vfio_pci.c | 10 ++++++++++ > include/linux/pci.h | 3 +++ > 3 files changed, 26 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 7e12d0163863..233cd4b5b6e8 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -2403,6 +2403,19 @@ void pcie_report_downtraining(struct pci_dev *dev) > if (PCI_FUNC(dev->devfn) != 0 || dev->is_virtfn) > return; > > + /* > + * If driver handles link_change event, defer to driver. PCIe drivers > + * can call pcie_print_link_status() to print current link info. > + */ > + device_lock(&dev->dev); > + if (dev->driver && dev->driver->err_handler && > + dev->driver->err_handler->link_change) { > + dev->driver->err_handler->link_change(dev); > + device_unlock(&dev->dev); > + return; > + } > + device_unlock(&dev->dev); > + > /* Print link status only if the device is constrained by the fabric */ > __pcie_print_link_status(dev, false); > } > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index cab71da46f4a..c9ffc0ccabb3 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -1418,8 +1418,18 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev, > return PCI_ERS_RESULT_CAN_RECOVER; > } > > +/* > + * Ignore link change notification, we can't differentiate signal related > + * link changes from user driver power management type operations, so do > + * nothing. Potentially this could be routed out to the user. > + */ > +static void vfio_pci_link_change(struct pci_dev *pdev) > +{ > +} > + > static const struct pci_error_handlers vfio_err_handlers = { > .error_detected = vfio_pci_aer_err_detected, > + .link_change = vfio_pci_link_change, > }; > > static struct pci_driver vfio_pci_driver = { > diff --git a/include/linux/pci.h b/include/linux/pci.h > index 27854731afc4..e9194bc03f9e 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -763,6 +763,9 @@ struct pci_error_handlers { > > /* Device driver may resume normal operations */ > void (*resume)(struct pci_dev *dev); > + > + /* PCIe link change notification */ > + void (*link_change)(struct pci_dev *dev); > }; > > >
