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[Xen-devel] XenServer Xen-4.5 (-rc3ish) testing


Over the weekend, XenServer testing managed to run a side-by-side test
of XenServer trunk and XenServer experimental xen-4.5.  These are
identical other than the version of Xen (and associated libraries) in
use, i.e. identical dom0 kernel, Xapi toolstack and dom0 userspace,
other than as linked against newer Xen libraries.

The Xen-4.5 tests were on top of c/s e6c3d371d4 "systemd: use pkg-config
to determine systemd library availability"

There are a few notable issues exposed:

XEN_DOMCTL_memory_mapping hypercall fails with EPERM where it didn't in
xen-4.4, given identical parameters.  The hypercall gained an extra
permission check as part of 0561e1f01e.  Our usecase here is a daemon in
dom0 mapping guest RAM to emulate a graphics card, but I currently don't
see how that is incompatible with the new permissions check.

Migrations from older Xens to Xen-4.5 fairly reliably crash domains (90%
of the time, both PV and HVM guests).  This includes migrates from older
XenServers using the legacy->v2 migration code which is confirmed-good
in "upgrade to Xen-4.4" case.  The migration v2 code in use is identical.

We have certain machines which are showing reliable failure to boot
under Xen-4.5, where they worked with 4.4.  Symptoms range from the dom0
kernel crashing before printing anything, to complaining that the initrd
is corrupt when attempting to decompress.  This appears to be hardware

I will be looking into all of these issues, to identify whether they are
indeed regressions in xen-4.5, or whether I have make some mistakes
forward porting our patch queue.

Unfortunately, our PCI Passthrough testing has been blocked behind other
regressions which have crept in recently, meaning that both sets of
tests were equally affected, and no 4.4 vs 4.5 comparison has been
possible at this time.  I hope this will be fixed by the next time I run
a similar pair of tests.


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