On Wed, Aug 01, 2012 at 06:07:07PM +0300, Nadav Har'El wrote:
> On Wed, Aug 01, 2012, Avi Kivity wrote about "Re: Nested kvm_intel broken on
> pre 3.3 hosts":
> > Right - it's not just kvm-as-a-guest that will trip on this. But
> > there's no point in everyone backporting it on their own. If you're
> > doing the backport, please post it here and we'll forward it to the
> > stable branch.
>
> If I understand correctly, the failure occurs because new versions of
> KVM refuse to work if the processor doesn't support CPU_BASED_RDPMC_EXITING -
> which older versions of nested VMX didn't say that they did.
>
> But must the KVM guest refuse to work if this feature isn't supported?
> I.e., why not move in setup_vmcs_config() the CPU_BASED_RDPMC_EXITING
> from "min" to "opt"? Isn't losing the PMU feature a lesser evil than
> not working at all? In any case, perhaps the original reporter can use
> this as a workaround, at least, because it requires modifying the (L1)
> guest, not the host.
>
>
Since L2 or L1 have to be fixed anyway for setup to work it is better to
fix L1 to work according to a spec than fixing L2 to workaround L1 bug.
--
Gleb.
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