On Wed, 10 Apr 2013 13:08:46 +0300 Gleb Natapov <gleb@xxxxxxxxxx> wrote: > On Wed, Apr 10, 2013 at 11:29:42AM +0200, Andre Przywara wrote: > > In a real world VendorSpecific should be replaced with something > > more meaningful. Depends on KVMs intention to emulate instructions, > > actually out of scope for a pure virtualizer. > > > Something like EmulateOnUD. Right. > > What is the opinion from the KVM folks on this? Shall we start to > > emulate instructions the host does not provide? In this particular > > case a relatively simple patch fixes a problem (starting Atom > > optimized kernels on non-Atom machines). > We can add the emulation, but we should not start announcing the > instruction availability to a guest if host cpu does not have it by > default. This may trick a guest into thinking that movbe is the > fastest way to do something when it is not. Good point. I'd also like to have a switch which enables this kind of "non-standard" behavior. Actually this should be requested by QEMU, right? So that a single guest can override the CPUID masking done by the kernel if it really really wants to. > > > > (And if one can believe the AMD Fam16h SWOG [1], PS4^Wfuture AMD > > processors have MOVBE, so it's not even actually one CPU anymore). > If a host CPU has the instruction emulation is not needed unless the > instruction is used for MMIO access. I meant to "emulate" such a CPU. -cpu ps4 ;-) Regards, Andre. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
