The issue is introduced in commit a0aec36, the following comment is from this path:

This patch fixes two problems:
        1) The device will be reattached to host even if it's not
           managed, as there is a "pciDeviceSetManaged".

And in codes:

1960 static int
1961 qemuDomainDetachHostPciDevice(struct qemud_driver *driver,
1962                               virDomainObjPtr vm,
1963                               virDomainDeviceDefPtr dev,
1964                               virDomainHostdevDefPtr *detach_ret)
1965 {
......
2026     pci = pciGetDevice(detach->source.subsys.u.pci.domain,
2027                        detach->source.subsys.u.pci.bus,
2028                        detach->source.subsys.u.pci.slot,
2029                        detach->source.subsys.u.pci.function);
2030     if (pci) {
2031         activePci = pciDeviceListSteal(driver->activePciHostdevs, pci);
2032         if (pciResetDevice(activePci, driver->activePciHostdevs, NULL))
2033             qemuReattachPciDevice(activePci, driver);
2034         else
2035             ret = -1;
2036         pciFreeDevice(pci);
2037         pciFreeDevice(activePci);
2038     } else {
2039         ret = -1;
2040     }
......

In fact, the function qemuReattachPciDevice will call pciDeviceGetManaged function, if the pci device isn't managed mode, it will directly return, so the pci devices can't also been reattached to host.

In addition, in line 2032, also should judge pciResetDevice function return value, if return value < 0, then XXXX and change ret = -1 etc.

Upstream commit 6be610bfaae08655eaf93f9638d4c6636c00343f fixed the problem indicentally.

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index dc40d2f..4b60839 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -2029,7 +2029,8 @@ qemuDomainDetachHostPciDevice(struct qemud_driver *driver,
                        detach->source.subsys.u.pci.function);
     if (pci) {
         activePci = pciDeviceListSteal(driver->activePciHostdevs, pci);
-        if (pciResetDevice(activePci, driver->activePciHostdevs, NULL))
+        if (pciResetDevice(activePci, driver->activePciHostdevs,
+                           driver->inactivePciHostdevs) == 0)
             qemuReattachPciDevice(activePci, driver);
         else
             ret = -1;

Hi Osier,
Although device detached successfully, the pci device can't be returned to host with managed mode, is this a expected result? I don't think so. I remember the original design is the pci device with managed mode will be automatically returned to host when detaching a hot-pluged pci device from running guest or shut down the running guest with attached pci device.

In addition, I tried to manually reattach the pci device to host, although virsh nodedev-reattach said Device pci_0000_00_19_0 re-attached, in fact, the pci device is /sys/devices/pci0000:00/0000:00:19.0/driver not original e1000e, I still can't use the NICs on host.

Thanks,
Alex

(In reply to comment #6)

> pci device is /sys/devices/pci0000:00/0000:00:19.0/driver not original e1000e,
s/device/driver/.

Hi Osier, 
I saw your v2 patch "qemu: Introduce inactive PCI device list" remove 'if (!pciDeviceGetManaged(dev))' judgement from 'qemuReattachPciDevice' function, I think the patch will fix some issues on Comment 6 not all, if 'pciResetDevice != 0', we should also do some cleanup work such as returning the pci device to host, right?

Alex

With comment 0 steps, on libvirt-0.9.10-1.el6.x86_64, results:

[root@zhpeng ~]# virsh attach-device kvm1 nodedev.xml 
Device attached successfully

[root@zhpeng ~]# virsh detach-device kvm1 nodedev.xml 
Device detached successfully

So it's verified.

libvirt-0.9.4-23.el6_2.6 test passed.

    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
No documentation needed.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2012-0748.html