On 27/04/2018 02:57, Junaid Shahid wrote: > On 04/26/2018 04:16 PM, Jim Mattson wrote: >> On Thu, Apr 26, 2018 at 3:43 PM, Junaid Shahid <junaids@xxxxxxxxxx> >> wrote: >>> When INVPCID is not supported, KVM should clear the INVPCID bit >>> from the guest CPUID. >> This seems to be the only guest CPUID bit that's verified in this >> way. That seems...odd. Why enforce this one constraint? > > Hmm. I wonder if the other bits are not validated intentionally, > perhaps to facilitate user-mode emulation? If that is the case, then > yes, we don't need to validate the INVPCID bit either. They are not validated mostly because it's pointless. Userspace is supposed to validate them against KVM_GET_SUPPORTED_CPUID, if it doesn't it's garbage-in garbage-out. INVPCID and others have some special casing because they require toggling some execution controls, but that's where those needs end. Thanks, Paolo
