KVM vs. PCI-E Function Level Reset (FLR) ...

[Casey Leedom <leedom@chelsio.com>]

  I've ground my way through most of the Linux kernel code supporting KVM and 
"Device Assignment" but I haven't been able to untangle the path of when/where 
PCI-E Function Level Resets (FLRs) are applied and what happens if the Virtual 
Machine OS/Driver attempts to perform an FLR on the PCI Pass Through Device.

  It looks like the Linux KVM kernel support code issues an FLR against an 
Assigned Device when the device is assigned and when it's freed but it's not 
clear when those actions are taken.  For instance, if a device is assigned to a 
VM and then the VM reboots itself, is that counted as another assignment point?  
I.e. will KVM issue a new pci_reset_function() on the device so it shows up 
reset in the newly rebooted VM?

  And what happens if the VM OS/Driver attempts to write the PCI Pass Through 
Device's PCI-E FLR bit?  I assume that that write (and the following polling 
reads) are trapped by the KVM code but I can't find the code which implements the 
PCI Configuration Space emulation to see if the FLR is implemented there.  For 
instance, if I run Linux 2.6.30 in the VM and my Device Driver calls 
pci_reset_function() in its "probe()" function will that result in a Device FLR?  
it doesn't appear to be the case ...

      Note that it's impossible for a Device Driver to call pci_reset_function()
      under Linux 2.6.31 and later because a call to device_lock() was added
      to pci_dev_reset() in chageset 8e9394ce on Feb 17, 2010 by Greg
      Kroah-Hartman.  This means that a call to pci_reset_function() in a
      device driver's "probe()" routine will result in an immediate deadlock.

  Thanks for any help and/or insight into these questions!

Casey