Re: [PATCH] vfio: Set PCI_DEV_FLAGS_ASSIGNED when assigning device to guest

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 2014-01-30 at 23:36 +0530, Bandan Das wrote:
> Alex Williamson <alex.williamson@redhat.com> writes:
> 
> > [cc +linux-pci]
> >
> > On Thu, 2014-01-30 at 10:33 -0700, Alex Williamson wrote:
> >> On Thu, 2014-01-30 at 22:54 +0530, Bandan Das wrote:
> >> > Some drivers such as ixgbe rely on pci_vfs_assigned() to prevent
> >> > disabling sr-iov when vfs are still assigned during hotplug
> >> > event or module removal. Set and unset PCI_DEV_FLAGS_ASSIGNED
> >> > appropriately
> >> 
> >> This flag has always felt like a band-aide for KVM device assignment
> >> because a device could be used without an actual driver attached to the
> >> device.  vfio-pci is an actual driver, so why should it matter whether
> >> the device is assigned or in use by ixgbevf or in use by pci-vfio?  It
> >> seems like sr-iov shouldn't be disabled so long as either a driver or
> >> this (needs to be deprecated) flag are set.  Thanks,
> 
> With cases such as vfio-pci, not having this flag set will disable sriov
> while a guest is using it resulting in a hung guest.

That sounds like a bug, why would a PF disable sr-iov while there's
still a driver attached to the VF?  Is the PF assuming the driver can
reconnect to the VF later or continue w/o a VF?  How can it make such an
assumption?

>  I am unfamiliar if 
> similar scenarios are applicable to other test cases. If the flag needs
> to be set, what's a better place then ? Or how does the PF driver decide not 
> to disable sr-iov, should it be based on - as long as the device is bound to 
> a driver ?

It seems like a better approach would be for drivers that are capable of
having the VF removed from under them to set a flag, which would allow
the PF driver to be told rather than assume it can disable sr-iov.  Then
it would be a feature flag rather than some made-up association with
device assignment.  Thanks,

Alex

> >> > ---
> >> >  drivers/vfio/pci/vfio_pci.c | 2 ++
> >> >  1 file changed, 2 insertions(+)
> >> > 
> >> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> > index 7ba0424..7cc7ed6 100644
> >> > --- a/drivers/vfio/pci/vfio_pci.c
> >> > +++ b/drivers/vfio/pci/vfio_pci.c
> >> > @@ -90,6 +90,7 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
> >> >  		vdev->has_vga = true;
> >> >  #endif
> >> >  
> >> > +	pdev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
> >> >  	return 0;
> >> >  }
> >> >  
> >> > @@ -149,6 +150,7 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
> >> >  				__func__, dev_name(&pdev->dev), ret);
> >> >  	}
> >> >  
> >> > +	pdev->dev_flags &= ~PCI_DEV_FLAGS_ASSIGNED;
> >> >  	pci_restore_state(pdev);
> >> >  }
> >> >  
> >> 
> >> 
> >
> >
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe kvm" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html