On 05.11.2013, at 17:16, Andreas Färber <afaer...@suse.de> wrote: > Am 05.11.2013 07:05, schrieb Alexander Graf: >> >> >> Am 05.11.2013 um 05:00 schrieb Paul Mackerras <pau...@samba.org>: >> >>> On Mon, Nov 04, 2013 at 10:05:58AM +0100, Alexander Graf wrote: >>>> >>>> Yeah, we really need to check that guest vpcu == host vcpu for HV KVM. >>> >>> In general I agree, but the one difficulty I see is that a check for >>> exact equality will interact badly with qemu's habit of picking a >>> specific processor version when the user specifies something general >>> like "POWER7". So if the user does -cpu POWER7 on a machine with >>> (for example) a POWER7 v2.1 processor, but qemu arbitrarily picks the >>> PVR for POWER7 v2.3, then it will fail, which will be completely >>> puzzling to the user -- "I asked for POWER7, and it is a POWER7, >>> what's the problem??". >>> >>> Maybe if the user asks for a non-specific processor type, and the >>> host's PVR matches the request, then qemu should take the host's PVR >>> rather than just picking some arbitrary processor version. >> >> Yup. > > But then it's no longer generally reproducible: "POWER7" won't be > "POWER7" on another machine. > > One thing I original did iirc was to hide the aliases from QMP. You can > always do stupid things on the command line and then we can blame you, > but if libvirt and upper layers don't offer "POWER7" to the end user > then we don't need to worry about the average user misinterpreting its > semantics.
We could also just be nice and error out with a sane error message: Your selected CPU POWER7_v10 is not compatible with the host's CPU POWER7_20 with your currently selected KVM mode. Please use the latter or -cpu host. Alex