Am 30.09.2011 um 09:50 schrieb David Gibson <da...@gibson.dropbear.id.au>:
> This series contains some patches which, when using KVM, gather > information about the capabilities of the host CPU and advertise them > to the guest system when using the pseries machine. Specifically it > does this for whether the CPU supports VMX, VSX and/or DFP > instructions, and for the CPUs supported page sizes. > > The VSX and DFP portions of this were posted earlier, and I've fixed > the minor comments which people made. This leaves one objection from > Alex Graf, that whether the features are advertised should also depend > on the target CPU selected in qemu. A similar objection may apply to > the pagesizes patch. I guess the idea is to "clamp" the advertised > capabilities to those permitted by the selected target CPU, but I'm > not entirely sure what the logic here should be. > > Frankly, particularly in the case of KVM Book3S-HV, I'm not terribly > convinced that attempting to make the guest CPU appear different from > the host CPU is terribly meaningful. These patches as they stand have > the advantage that future, roughly compatible CPUs should Just Work > with these capabilities advertised in the correct cases. Alex, can > you advise what sort of logic you'd like here. Yes, very simple. I want you to create a CPU type 'host', similar to how x86 does it. That should be the default CPU type for KVM with the pseries machine. You can also add a check in-kernel that verifies if guest PVR == host PVR for HV mode. That way you ensure that -cpu host is always used there. If you later add compat modes, you can check them there, but still have -cpu xxx available to tell all pieces of the kvm/qemu chain what to use. Alex
