On Wednesday 14 July 2010 04:41:01 Casey Leedom wrote:
> 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?
The assignment/deassignment happened when guest was created/destroyed. Currently
it wouldn't issue a FLR when guest reset.
> 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 ...
The PCI configuration space emulated is in QEmu rather than KVM. You can check
qemu-kvm/hw/device-assignment.c. We didn't emulate FLR capability now. (OK, some
other device specific reset method may involved, you can check pci_dev_reset())
> 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.
What I saw the code is like this:
static int pci_dev_reset(struct pci_dev *dev, int probe)
{
int rc;
might_sleep();
if (!probe) {
pci_block_user_cfg_access(dev);
/* block PM suspend, driver probe, etc. */
device_lock(&dev->dev);
}
[...]
So seems it's fine with _probe_ set, to use with probe() routine.
--
regards
Yang, Sheng
>
> Thanks for any help and/or insight into these questions!
>
> Casey
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