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

Ethan Zhao
2014-07-21T03:17:10Z

On Mon, Jul 21, 2014 at 9:58 AM, Alex Williamson
<alex.williamson@redhat.com> wrote:
> On Sun, 2014-07-20 at 14:48 +0000, Yuval Mintz wrote:
>> > On Fri, 2014-07-11 at 07:13 -0600, Alex Williamson wrote:
>> > > On Fri, 2014-07-11 at 20:30 +0800, Ethan Zhao 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...

Thanks,
Ethan

>
> Alex
>

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