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

[Duyck, Alexander H]

We could do that. It shouldn't be an issue as long as we disable SR-IOV first.

It would just be a matter of recording the state of kernel_pf_autoprobe vs user_pf_autoprobe. It might be useful to make that distinction in the comments somewhere in the code and in the patch description.

- Alex

> -----Original Message-----
> From: Wang, Liang-min
> Sent: Monday, December 11, 2017 6:23 AM
> To: Alex Williamson <alex.williamson@xxxxxxxxxx>; Alexander Duyck
> <alexander.duyck@xxxxxxxxx>
> Cc: Kirsher, Jeffrey T <jeffrey.t.kirsher@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
> 
> 
> 
> > -----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