Re: [PATCH 1/2 V3] PCI: introduce device assignment interface and refactory related code

Alex Williamson
2014-07-21T14:01:13Z

On Mon, 2014-07-21 at 13:17 +0000, Yuval Mintz wrote:
> > >> > > > This patch introduces two new device assignment functions
> > >> > > >
> > >> > > > pci_iov_assign_device(),
> > >> > > > pci_iov_deassign_device()
> > >> > > >
> > >> > > > along with the existed one
> > >> > > >
> > >> > > > pci_vfs_assigned()
> > >> > > >
> > >> > > > They construct the VFs assignment management interface, used to
> > >> > > > assign/ deassign device to VM and query the VFs reference counter.
> > >> > > > instead of direct manipulation of device flag.
> > >>
> > >> Sorry for the late intrusion into the conversation, and perhaps it's
> > >> a bit unrelated, but given that you're creating a 'VF assignment management'
> > >> perhaps it's the right place to add some sort of mechanism in order
> > >> to prevent module removal once one of its VFs is assigned.
> > >> [e.g., incrementing module reference count]
> > >>
> > >> At the moment [to the best of my knowledge] there's no mechanism
> > >> preventing the 'not-so-bright' user from removing the driver, and no
> > >> good will come out of it.
> > >
> > > On what module would the reference count be increased, the PF? The
> > > entire "VF assigned" interface is a hack to work around poor
> > > architectures like legacy KVM device assignment where there's no
> > > proper device owner for the VF. This is "fixed" by using VFIO instead
> > > and hopefully deprecating legacy KVM assignment. Thanks,
> >
> > To explain what Alex said, in another word, if VMs access VF via VFIO driver,
> > the owner of the device is VFIO, in this case, if you unload PF driver, you still
> > need to unload VFIO first, then unload PF driver. but the PF driver knows how to
> > notify the VFIO driver to unload.
> > But without VFIO like driver, for example some of current code will assign
> > devcie (PF/VF) directly to KVM or XEN without driver in the middle. and the PF
> > driver doesn't know how to unbind the assignment...
>
> Hi,
>
> I thought about perhaps incrementing the reference count of the PF's module
> [i.e., the module supplying the driver for the PF] directly, so THAT module won't
> be removable as long as the VF is assigned.
>
> Although I don't know whether the module is even accessible; Can you derive a
> pointer to a module from a net_device struct?

A VF is not necessarily a net device. A pci_dev does have a physfn
pointer though.

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