On 2012-10-18 08:29, Paolo Bonzini wrote: > Il 17/10/2012 20:37, Jan Kiszka ha scritto: >> On 2012-10-17 18:44, Paolo Bonzini wrote: >>> Il 17/10/2012 18:37, Clemens Kolbitsch ha scritto: >>>> Guys, >>>> >>>> I know this is question might seem a bit odd, but I'm curious: >>>> >>>> Has anyone ever tried to write code to disable KVM on the fly / is it >>>> at all possible? I have a situation where I need to use TCG for >>>> certain parts of the code, but would love to have acceleration for >>>> everything else. My idea was to pause the VM, then use the >>>> snapshotting mechanism to dump the state, and then to resume the >>>> snapshot, but writing the KVM state into the non-KVM structures. >>> >>> As a start, you can try using "migrate exec:cat>foo.save" with a KVM >>> machine and "-incoming 'exec:cat foo.save'" with a TCG machine. The >>> main problem should be that TCG doesn't implement kvmclock. >>> >>> If you disable the KVM interrupt controller and timer (which is just an >>> implementation detail, not a hardware difference), >> >> Unnecessary. Both models (KVM in-kernel and QEMU userspace) are >> compatible - in the absence of bugs. > > He wants to really switch it on the fly---not just migrate out and > in---and for that you need to disable the KVM-specific devices.
Well, that's even more unrealistic than via migration. > >> But loading a KVM image into TCG lets non-trival guests lock up. Likely >> due to differences in the CPU virtualization/emulation (MSRs...). > > Perhaps that can be mitigated by using an older machine model. Start > with something simple like a pentium2 and work up from there... Even if, there are still too many untranslated, maybe even untranslatable states of the KVM CPU model, at least. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux
