On 12/19/2011 04:11 PM, Jan Kiszka wrote:
Backwards compatibility
If we want backwards compatibility, we need more than just a simple feature
check, no? Oh, you feed that into CPUID? That's nifty. Ok, so you behave like
VMX/SVM do on real hardware - you always expose the functionality but don't
list it in CPUID for older user space.
Do we want this to be on when providing a compat machine type ("pc-0.12"
etc.) to the guest? Then it does need more work (see the dance around
kvmclock).
We do. I have a feeling the whole cpuid stuff, paravirt and
non-paravirt, needs some fixing in this area. It's different than the
normal compat code since not only qemu, but also kvm and the host cpu
have a say in what's supported and what's not.