linux-kernel - Re: [PATCH 1/1] vfio-pci: Add SR-IOV VF configuration via sysfs

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Date:	Wed, 01 Oct 2014 08:47:06 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Andre Richter <andre.o.richter@...il.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] vfio-pci: Add SR-IOV VF configuration via sysfs

On Wed, 2014-10-01 at 16:28 +0200, Andre Richter wrote:
> I currently use it for early development/debugging work (SR-IOV
> capable FPGA boards) where I test both PFs and VFs from userspace.
> But I see your point that this may not be relevant for anything you
> can buy off the shelf.

What about adding the same to pci-stub?  At least that way the PF can't
actually be assigned to a guest via vfio.  Legacy KVM assignment would
still allow it, but then legacy KVM assignment will attempt to assign a
device regardless of the host driver.  BTW, I'd expect there also needs
to be a call to pci_disable_sriov() in the driver release function.
Thanks,

Alex

> 2014-10-01 16:03 GMT+02:00 Alex Williamson <alex.williamson@...hat.com>:
> > On Wed, 2014-10-01 at 15:38 +0200, Andre Richter wrote:
> >> If a PCIe device bound to vfio-pci happens to be SR-IOV capabale,
> >> there is no possibility to bring up/shutdown the device's VFs.
> >>
> >> This patch adds a generic callback for the sysfs sriov_numvfs attribute.
> >> The attribute will only show up for SR-IOV devices. Additionally,
> >> each utilized pci_* function checks if the device is a PF.
> >>
> >> Signed-off-by: Andre Richter <andre.o.richter@...il.com>
> >> ---
> >>  drivers/vfio/pci/vfio_pci.c | 25 ++++++++++++++++++++-----
> >>  1 file changed, 20 insertions(+), 5 deletions(-)
> >
> > I don't understand why you'd want to do this.  The PF is typically
> > managed by a host driver.  By allowing vfio-pci to manage SR-IOV, don't
> > we potentially have assign-able PFs managing assign-able VFs?  That
> > seems like a bad idea.  What use case do you have in mind?  Thanks,
> >
> > Alex
> >
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index f782533..2f6dfb3 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -919,12 +919,27 @@ static struct pci_error_handlers vfio_err_handlers = {
> >>       .error_detected = vfio_pci_aer_err_detected,
> >>  };
> >>
> >> +static int vfio_pci_sriov_configure(struct pci_dev *pdev, int num_vfs)
> >> +{
> >> +     int ret = 0;
> >> +
> >> +     if (num_vfs > 0) {
> >> +             ret = pci_enable_sriov(pdev, num_vfs);
> >> +             if (!ret)
> >> +                     ret = pci_num_vf(pdev);
> >> +     } else
> >> +             pci_disable_sriov(pdev);
> >> +
> >> +     return ret;
> >> +}
> >> +
> >>  static struct pci_driver vfio_pci_driver = {
> >> -     .name           = "vfio-pci",
> >> -     .id_table       = NULL, /* only dynamic ids */
> >> -     .probe          = vfio_pci_probe,
> >> -     .remove         = vfio_pci_remove,
> >> -     .err_handler    = &vfio_err_handlers,
> >> +     .name                   = "vfio-pci",
> >> +     .id_table               = NULL, /* only dynamic ids */
> >> +     .probe                  = vfio_pci_probe,
> >> +     .remove                 = vfio_pci_remove,
> >> +     .sriov_configure        = vfio_pci_sriov_configure,
> >> +     .err_handler            = &vfio_err_handlers,
> >>  };
> >>
> >>  /*
> >
> >
> >



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