[Pkg-libvirt-maintainers] Bug#773189: libvirt-daemon: Haswell microcode update breaks CPU detection

[intrigeri]

hi,

Chris Boot wrote (15 Dec 2014 12:39:52 GMT) :
> The intel-microcode 3.20140913.1 update disables TSX-NI (transactional
> memory instructions). When a server running libvirt is rebooted with
> this update, libvirt no longer considers the machine to have a Haswell
> CPU:

> dietrich ~ # virsh capabilities | grep -A1 '<arch>x86_64'
>       <arch>x86_64</arch>
>       <model>SandyBridge</model>

> This causes a problem as any VMs that require a Haswell CPU, which would
> have worked previously, now fail to start altogether. Commenting out the
> two cpuinfo flags relevant to TSX-NI from /usr/share/libvirt/cpu_map.xml
> fixes this for me:

FWIW, I've been suffering from the symptoms of that issue for a few
weeks. I guessed it was caused by that microcode update, but had no
time to report it. *If* that's a regression since Wheezy, I think
it would qualify as RC, since VMs that started just fine previously
now fail to come up at boot. The workaround (in the package) is tiny,
and makes sense to me: if Intel themselves now consider that Haswell
CPUs have no TSX-NI, then libvirt's view of what's a Haswell CPU
should be updated.

OTOH, the user-side workaround (copy host CPU model) is easy enough
too, although a bit painful to discover initially for many users
I guess.

Shall we ask the release team if they would happily unblock this
change for Jessie?