Re: Results from the Xen 4.4-rc2 test day

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 21/01/14 10:28, Andrew Cooper wrote:
> Hello,
>
> I participated in (a rather extended version of) the 4.4-rc2 test day,
> and rc2 got a full XenRT nightly run in the XenServer testing system.
>
> For the setup, the comparison is against XenServer trunk, which is
> currently Xen-4.3-staging based (plus patch queue), Linux 3.10.y dom0
> kernel, CentOS 6.4 based dom0 userspace.
>
> The tested version had Xen 4.4 (staging, as I needed the ABI fix) in
> place of Xen-4.3, but identical dom0 kernel, dom0 userspace, qemu,
> toolstack and windows PV drivers.
>
>
> The major issue identified is with Windows 8/8.1 and Server 2012/2012r2,
> which have problems on live migrate.  Some source of time is
> unexpectedly jumping forwards by two days, from the correct time to 2
> days in the future.  The observed result is that it looses its DHCP
> lease, drops its IP address and networking ceases to work (It appears
> that windows will not attempt to renew the lease itself).
>

This is caused by commit e36cd2cdc9674a7a4855d21fb7b3e6e17c4bb33b
"x86/viridian: Time Reference Count MSR"

After double checking with the specification, it does appear to be
implemented as required (subject to a potential issue with multiple vcpu
guests).

I am currently experimenting to see whether hvm_get_guest_time() is
returning unexpected values, or whether it is returning expected values
and Windows is interpreting them differently.

At this point in the 4.4 release cycle, reverting the patch should be
seriously considered, although I would like to see whether it is
possible to work out why it is wrong and whether there is an obvious fix
first.

~Andrew