[Xen-devel] Xen 4.1 rc5 outstanding bugs

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi all,
I went through the list of bugs affecting the latest Xen 4.1 RC and
I made a list of what they seem to be the most serious.
All of them affect PCI passthrough and seem to be hypervisor/qemu-xen
bugs apart from the last one that is a libxenlight/xl bug.


 *  VF passthrough does not work
Passing through a normal NIC seem to work but passing through a VF
doesn't.
The device appears in the guest but it cannot exchange packets, the
guest kernel version doesn't seem to matter.
>From the qemu logs:

pci_msix_writel: Error: Can't update msix entry 0 since MSI-X is already        
         function.

It might be the same problem of the two following bug reports:
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1709
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1742


 *  Xen panic on guest shutdown with PCI Passthrough
http://xen.1045712.n5.nabble.com/Xen-panic-on-guest-shutdown-with-PCI-Passthrough-tt3371337.html#none
When the guest with a passthrough pci device is shut down, Xen panic
on a NMI - MEMORY ERROR.
(XEN) Xen call trace:
(XEN)    [<ffff82c48015f032>] msi_set_mask_bit+0xea/0x121
(XEN)    [<ffff82c48015f087>] mask_msi_irq+0xe/0x10
(XEN)    [<ffff82c480162fb1>] __pirq_guest_unbind+0x298/0x2aa
(XEN)    [<ffff82c48016315c>] unmap_domain_pirq+0x199/0x307
(XEN)    [<ffff82c480163321>] free_domain_pirqs+0x57/0x83
(XEN)    [<ffff82c48015642a>] arch_domain_destroy+0x30/0x2e3
(XEN)    [<ffff82c480104c59>] complete_domain_destroy+0x6e/0x12a
(XEN)    [<ffff82c48012adfd>] rcu_process_callbacks+0x173/0x1e1
(XEN)    [<ffff82c480123327>] __do_softirq+0x88/0x99
(XEN)    [<ffff82c4801233a2>] do_softirq+0x6a/0x7a


 *  possible Xen pirq leak at domain shutdown
If a guest doesn't support pci hot-unplug (or a malicious guest), it
won't do anything in response to the acpi SCI interrupt we send when the
domain is destroyed, therefore unregister_real_device will never be
called in qemu and we might be leaking MSIs in the Xen (to be
verified).
http://xen.1045712.n5.nabble.com/template/NamlServlet.jtp?macro=print_post&node=3369367


 *  Xen warns about MSIs when assigning a PCI device to a guest
also known as "Xen complains msi error when startup"
At startup Xen prints multiple:
(XEN) Xen WARN at msi.c:635
(XEN) Xen WARN at msi.c:648
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1732


 *  PCI hot-unplug causes a guest crash
also know as "fail to detach NIC from guest"
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1736


 * multiple PCI devices passthrough to PV guests or HVM guests with
   stubdoms is broken with the xl toolstack
Cannot assign >1 PCI passthrough devices as domain creation time because
libxl creates a bus for the first device and increments "num_devs" node
in xenstore for each subsequent device but pciback cannot cope with
num_devs changing while the guest is not running to respond to the
reconfiguration request. A fix would be to create the entire bus in a
single cold-plug operation at start of day.



 - Stefano

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