Guest CPU definitions with mode='custom' and missing <vendor> are
expected to run on a host CPU from any vendor as long as the required
CPU model can be used as a guest CPU on the host. But even though no CPU
vendor was explicitly requested we would sometimes force it due to a bug
in virCPUUpdate and virCPUTranslate.
The bug would effectively forbid cross vendor migrations even if they
were previously working just fine.
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
The reworked API is now called virCPUUpdate and it should change the
provided CPU definition into a one which can be consumed by the QEMU
command line builder:
- host-passthrough remains unchanged
- host-model is turned into custom CPU with a model and features
copied from host
- custom CPU with minimum match is converted similarly to host-model
- optional features are updated according to host's CPU
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
There's no reason for keeping the features in a linked list. Especially
when we know upfront the total number of features we are loading.
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
The mode can be either of "custom" (default), "host-model",
"host-passthrough". The semantics of each mode is described in the
following examples:
- guest CPU is a default model with specified topology:
<cpu>
<topology sockets='1' cores='2' threads='1'/>
</cpu>
- guest CPU matches selected model:
<cpu mode='custom' match='exact'>
<model>core2duo</model>
</cpu>
- guest CPU should be a copy of host CPU as advertised by capabilities
XML (this is a short cut for manually copying host CPU specification
from capabilities to domain XML):
<cpu mode='host-model'/>
In case a hypervisor does not support the exact host model, libvirt
automatically falls back to a closest supported CPU model and
removes/adds features to match host. This behavior can be disabled by
<cpu mode='host-model'>
<model fallback='forbid'/>
</cpu>
- the same as previous returned by virDomainGetXMLDesc with
VIR_DOMAIN_XML_UPDATE_CPU flag:
<cpu mode='host-model' match='exact'>
<model fallback='allow'>Penryn</model> --+
<vendor>Intel</vendor> |
<topology sockets='2' cores='4' threads='1'/> + copied from
<feature policy='require' name='dca'/> | capabilities XML
<feature policy='require' name='xtpr'/> |
... --+
</cpu>
- guest CPU should be exactly the same as host CPU even in the aspects
libvirt doesn't model (such domain cannot be migrated unless both
hosts contain exactly the same CPUs):
<cpu mode='host-passthrough'/>
- the same as previous returned by virDomainGetXMLDesc with
VIR_DOMAIN_XML_UPDATE_CPU flag:
<cpu mode='host-passthrough' match='minimal'>
<model>Penryn</model> --+ copied from caps
<vendor>Intel</vendor> | XML but doesn't
<topology sockets='2' cores='4' threads='1'/> | describe all
<feature policy='require' name='dca'/> | aspects of the
<feature policy='require' name='xtpr'/> | actual guest CPU
... --+
</cpu>
In case a hypervisor doesn't support the exact CPU model requested by a
domain XML, we automatically fallback to a closest CPU model the
hypervisor supports (and make sure we add/remove any additional features
if needed). This patch adds 'fallback' attribute to model element, which
can be used to disable this automatic fallback.
