On Tue, Dec 16, 2014 at 02:47:24PM +0000, Daniel P. Berrange wrote:
On Tue, Dec 16, 2014 at 03:37:06PM +0100, Guido Günther wrote:
On Tue, Dec 16, 2014 at 12:40:26PM +0000, Daniel P. Berrange wrote:
On Tue, Dec 16, 2014 at 01:33:15PM +0100, Guido Günther wrote:
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:
# virsh capabilities | grep -A1 '<arch>x86_64' <arch>x86_64</arch> <model>SandyBridge</model>
Since Intel disables the feature on their CPUs we shouldn't check for it as well to keep VMs using Haswell working.
This was debugged and reported by Chris Boot at http://bugs.debian.org/773189 --- src/cpu/cpu_map.xml | 1 - 1 file changed, 1 deletion(-)
diff --git a/src/cpu/cpu_map.xml b/src/cpu/cpu_map.xml index bd9b056..f41dbce 100644 --- a/src/cpu/cpu_map.xml +++ b/src/cpu/cpu_map.xml @@ -507,7 +507,6 @@ <feature name='movbe'/> <feature name='fsgsbase'/> <feature name='bmi1'/> - <feature name='hle'/> <feature name='avx2'/> <feature name='smep'/> <feature name='bmi2'/>
NACK. We can not change existing models in cpu_map.xml because that results in a guest ABI change.
But Intel changed the ABI as well by removing hle so what would we do to move forward? Introduce another model? This would still break systems with the microcode update.
Simply do nothing. There is no requirement that guest CPU model names match the host CPU you are running on. A guest CPU model name is simply a synonym for a collection of features. If libvirt reports 'SandyBridge' for the host CPU model, when it is in fact 'Hasmere' that's not a serious problem, because the key fact is that the feature bits are correctly detected regardless of what name is reported.
But this means that VMs that have e.g. <cpu mode='custom' match='exact'> <model fallback='forbid'>Haswell</model> <vendor>Intel</vendor> ... </cpu> refuse to start after the microcode upgrade like error: Failed to start domain foo error: unsupported configuration: guest and host CPU are not compatible: Host CPU does not provide required features: hle Following your argument this makes a lot of sense since the feature isn't in the set of supported features anymore. From a users perspective it's confusing since they have a Haswell CPU built in still. So should we define a Haswell2 cpu type without hle so users can select it in case they don't want to use 'host-model'? Cheers, -- Guido