Eduardo Habkost wrote: > On Fri, Mar 23, 2012 at 03:49:27AM +0000, Liu, Jinsong wrote: >> Eduardo Habkost wrote: >>> [1] From Documentation/virtual/kvm/api.txt: >>> >>> "KVM_GET_SUPPORTED_CPUID >>> [...] >>> This ioctl returns x86 cpuid features which are supported by both >>> the hardware and kvm. Userspace can use the information returned >>> by this ioctl to construct cpuid information (for KVM_SET_CPUID2) >>> that is consistent with hardware, kernel, and userspace >>> capabilities, and with >>> ^^^^^^^^^^^^^^^^^^^^^^^^^^ >>> user requirements (for example, the user may wish to constrain cpuid >>> to emulate older hardware, or for feature consistency across a >>> cluster)." >> >> The fixbug patch is implemented by Jan and Avi, I reply per my >> understanding. > > No problem. I hope Jan or Avi can clarify this. > >> >> I think for tsc deadline timer feature, KVM_CAP_TSC_DEADLINE_TIMER is >> slightly better than KVM_GET_SUPPORTED_CPUID. If use >> KVM_GET_SUPPORTED_CPUID, it means tsc deadline features bind to host >> cpuid, while it fact it could be pure software emulated by kvm >> (though currently it implemented as bound to hareware). For the sake >> of >> extension, it choose KVM_CAP_TSC_DEADLINE_TIMER. > > There's no requirement for GET_SUPPORTED_CPUID to be a subset of the > host CPU features. If KVM can completely emulate the feature by > software, then it can return the feature on GET_SUPPORTED_CPUID even > if the host CPU doesn't have the feature. That's the case for x2apic, > for example (see commit 0d1de2d901f4ba0972a3886496a44fb1d3300dbd). Jan/Avi, Could you elaborate more your thought? Thanks, Jinsong-- 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
