RE: [PATCH v2] Enable SR-IOV instantiation through /sys file

[Wang, Liang-min]

> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Friday, December 08, 2017 6:35 PM
> To: Alexander Duyck <alexander.duyck@xxxxxxxxx>
> Cc: Kirsher, Jeffrey T <jeffrey.t.kirsher@xxxxxxxxx>; Wang, Liang-min <liang-
> min.wang@xxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; Duyck,
> Alexander H <alexander.h.duyck@xxxxxxxxx>
> Subject: Re: [PATCH v2] Enable SR-IOV instantiation through /sys file
> 
> On Fri, 8 Dec 2017 15:19:18 -0800
> Alexander Duyck <alexander.duyck@xxxxxxxxx> wrote:
> 
> > On Fri, Dec 8, 2017 at 2:58 PM, Alex Williamson
> > <alex.williamson@xxxxxxxxxx> wrote:
> > > On Fri,  8 Dec 2017 13:47:58 -0800
> > > Jeff Kirsher <jeffrey.t.kirsher@xxxxxxxxx> wrote:
> > >
> > >> From: Liang-Min Wang <liang-min.wang@xxxxxxxxx>
> > >>
> > >> When a SR-IOV capable device is bound with vfio-pci, the
> > >> device loses capability of creating SR-IOV instances through /sy/bus/
> > >> pci/devices/.../sriov_numvfs. This patch re-activates this capability
> > >> for a PCIe device that is SR-IOV capable and is bound with vfio-pci.ko.
> > >> This patch also disables drivers_autoprobe attribute of SR-IOV devices
> > >> created from vfio-pci bound device by default, so user-space PF device
> > >> can coordinate the bring-up of SR-IOV devices
> > >>
> > >> Signed-off-by: Liang-Min Wang <liang-min.wang@xxxxxxxxx>
> > >> ---
> > >>  drivers/pci/pci-driver.c    | 12 ++++++++++++
> > >>  drivers/vfio/pci/vfio_pci.c | 22 ++++++++++++++++++++++
> > >>  include/linux/pci.h         |  1 +
> > >>  3 files changed, 35 insertions(+)
> > >>
> > >> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > >> index 7f47bb7..19522fe 100644
> > >> --- a/drivers/pci/pci-driver.c
> > >> +++ b/drivers/pci/pci-driver.c
> > >> @@ -1467,6 +1467,18 @@ void pci_dev_put(struct pci_dev *dev)
> > >>  }
> > >>  EXPORT_SYMBOL(pci_dev_put);
> > >>
> > >> +/**
> > >> + * pci_dev_sriov_autoprobe_set - set device sriov driver autoprobe
> > >> + * @dev: device with which sriov autoprobe will be set
> > >> + *
> > >> + */
> > >> +void pci_dev_sriov_autoprobe_set(struct pci_dev *dev, bool autoprobe)
> > >> +{
> > >> +     if (dev && dev->sriov)
> > >> +             dev->sriov->drivers_autoprobe = autoprobe;
> > >> +}
> > >> +EXPORT_SYMBOL(pci_dev_sriov_autoprobe_set);
> > >
> > > _GPL?
> > >
> > > It'd also be best to separate the pci and vfio changes into different
> > > patches.  Bjorn would need to at least ack this PCI interface.
> > >
> > >> +
> > >>  static int pci_uevent(struct device *dev, struct kobj_uevent_env *env)
> > >>  {
> > >>       struct pci_dev *pdev;
> > >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > >> index f041b1a..004836c 100644
> > >> --- a/drivers/vfio/pci/vfio_pci.c
> > >> +++ b/drivers/vfio/pci/vfio_pci.c
> > >> @@ -1213,6 +1213,8 @@ static int vfio_pci_probe(struct pci_dev *pdev,
> const struct pci_device_id *id)
> > >>               return -ENOMEM;
> > >>       }
> > >>
> > >> +     /* disable sriov automatic driver attachment */
> > >> +     pci_dev_sriov_autoprobe_set(pdev, false);
> > >
> > > This looks stateful, VF autoprobe is not restored on release.  Also,
> > > how would we know the initial state to restore it to?
> >
> > The initial state is whatever the user set it to. It is something that
> > can be toggled on and off via sysfs, and it defaults to true at
> > initialization. In this case we are opting to toggle it off when VFIO
> > is attached to the device. Restoring it after unloading the driver
> > might be even more confusing since it is something the user could
> > toggle at any time so a restore would end up overwriting that.
> 
> I'm not really willing to sign up for the inevitable bug reports when
> users can't figure out how to make their VFs work again in the host
> after they've used the PF for userspace drivers with vfio-pci.  I
> agree, both options are confusing, how do we make it not confusing?
> Can PCI core reset the autoprobe attribute to the default at some
> obvious point?  Thanks,
> 

I would like to confirm the scenario discussed here is to unload PF driver, right?
Since users need to release all SR-IOV from PF driver first before PF driver is
released, does it make sense to restore autoprobe when VFs are released?

> Alex