On Sun, Feb 21, 2010 at 05:07:45PM +0200, Avi Kivity wrote:
> On 02/21/2010 04:43 PM, Joerg Roedel wrote:
>> Difficult. We could use an instruction intercept which has no side
>> effect on guest state (invlpg for example).
>
> Especially as the guest might disable it and BUG() if npt is enabled.
>
>> But thats a lot more
>> dangerous than an INTR intercept. What about PENDING_INTERRUPT? Are
>> there hypervisors that may get confused getting this intercept without
>> asking for it?
>>
>
> That will likely confuse kvm, it means interrupts are not blocked so it
> is okay to inject one, and if the guest is running with interrupts
> disabled then the next entry will fail.
Completly different idea:
1. Give userspace an ioctl to freeze the complete VM (all vcpus must be
stopped afterwards)
2. The freeze routine does the following:
freeze_vm(...)
{
stop_all_vcpus();
for_each_vcpu(vcpu)
kvm_x86_ops->freeze_vcpu(vcpu);
}
The module specific freeze_vcpu function can save the nested state
inside the guests memory (vmcs area for nested-vmx and hsave area for
nested-svm). When no vcpu is running anymore this is save.
After migration the information is restored from there before any vcpu
is started again.
unfreeze_vm(...)
{
for_each_vcpu(vcpu)
kvm_x86_ops->unfreeze_vcpu(vcpu);
restart_all_vcpus();
}
In the SVM case this still leaves the problem that the MSR bitmap must
be read again from guests memory on unfreeze but that is not a real
problem.
Joerg
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