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

On Mon, Dec 08, 2014 at 07:03:19PM +0000, Andrew Cooper wrote:
> Hi,

Hey Andrew!
> 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.

I presume the daemon also does 'XEN_DOMCTL_iomem_permission' to grant
the other domain access to its RAM? And before it makes the
XEN_DOMCTL_memory_mapping hypercall.

> 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.

The XenServer is not using the in-the-tree migration system except in
the older version of XenServer right?
> 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
> specific.

Hardware specific is good. Could you give some ideas of what make/model
this is?

> 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.

<nods> Thank you!
> ~Andrew

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