On Wed, Apr 10, 2013 at 12:39:01PM +0200, Andre Przywara wrote: > 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. > Right, the question is how kernel can tell QEMU that the cpuid bit is supported but should not be set unless explicitly asked by an user. > > > > > > (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 ;-) > Ah, OK. -- Gleb. -- 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
