[Bug 47451] New: need to re-load driver in guest to make a hot-plug VF work

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=47451

           Summary: need to re-load driver in guest to make a hot-plug VF
                    work
           Product: Virtualization
           Version: unspecified
    Kernel Version: 3.5.0
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
        AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
        ReportedBy: yongjie.ren@intel.com
        Regression: Yes


Environment:
------------
Host OS (ia32/ia32e/IA64):ia32e
Guest OS (ia32/ia32e/IA64):ia32e
Guest OS Type (Linux/Windows):Linux (RHEL6u3)
kvm.git Commit:37e41afa97307a3e54b200a5c9179ada1632a844(master branch)
qemu-kvm Commit:28c3a9b197900c88f27b14f8862a7a15c00dc7f0(master branch)
Host Kernel Version:3.5.0-rc6  (Also exists in 3.6.0-rc3)
Hardware:Romley-EP (SandyBridge system)


Bug detailed description:
--------------------------
After hot plugging a VF to a Linux guest (e.g.RHEL6.3) in qemu monitor, the VF
cannot work in the guest by. I need to remove the VF driver (e.g. igbvf,
ixgbevf) and probe it again, then the VF can work in guest.
NIC: Intel 82599 NIC, Intel 82576 NIC

It needn't reload VF driver in hot-plug case when using an old kernel.
It's a regression in kernel. (commits are in kvm.git and qemu-kvm.git tree)
kvm      + qemu-kvm =result
37e41afa + 28c3a9b1 =bad
322728e5 + 28c3a9b1 =good

Note:
1. When assigning a VF in qemu-kvm command line (not hot-plug), VF can work
fine after boot-up.
2. It's easier to reproduce this in guest with 512/1024MB memory and 1/2 vCPUs.
3. Can't always reproduce with 2048MB and 2vCPUs. (Not very stable.)

Reproduce steps:
----------------
1.start up a host with kvm
2.qemu-system-x86_64 -m 512 smp 2 –net none –hda /root/rhel6u3.img
3.switch to qemu monitor  (ctrl+Alt+2)
4.device_add pci-assign,host=02:10.0,id=mynic   (02:10.0 is VF's BDF number.)
5.switch to guest  (ctrl+Alt+1)
6.check network of the VF.  (it can't work)
7. remove VF driver in guest ('rmmod igbvf')
8. re-probe VF driver in guest ('modprobe igbvf')
9. check network of the VF. (It should work this time.)


Current result:
----------------
The VF cannot work in the guest by default. Need to re-load VF driver in guest.

Expected result:
----------------
VF works well in the guest by default after hot-plug.

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