Re: [Qemu-devel] SR-IOV PF reset and QEMU VFs VFIO passthrough

[Alex Williamson]

On Sat, 2013-06-01 at 14:13 +0200, Benoît Canet wrote:
> Hello,
> 
> I may have soon the PF driver of an SR-IOV card to code and make work with
> QEMU/KVM so I have the following questions.
> 
> In an AMD64 setup where QEMU use VFIO to passthrough the VFs of an SR-IOV card
> to a guest will the consequences of a PF FLR be handled fine by QEMU and the
> guest ?
> 
> I read that pci_reset_function would call pci_restore_state restoring the 
> SR-IOV
> configuration after the reset of the PF.
> 
> The ways the hardware work means that the VFs would disappear and reappear in 
> a
> short lapse of time.
> 
> Will these events be handled by the kernel pci hotplug code ?
> 
> Given that the PF driver restore the PF config space after the reset will /sys
> files used by QEMU disappear and reappear messing the QEMU VFIO passthrough or
> will it goes smoothly ?

On an Intel 82576 SR-IOV NIC, a FLR of the PF does not cause the VFs to
be removed.  It's not clear to me that they continue working across the
reset, but there is no hotplug.  If there was a hotplug, vfio-pci won't
release the device while it's in use, so the hotplug would be blocked
until the devices becomes unused, such as from the VM being shutdown.
Thanks,

Alex