On Sat, Aug 16, 2025, David Woodhouse wrote: > In https://lkml.org/lkml/2008/10/1/246 VMware proposed a generic standard > for harmonising CPUID between hypervisors. It was mostly shot down in > flames, but the generic timing leaf at 0x4000_0010 didn't quite die. > > Mostly the hypervisor leaves at 0x4000_0xxx are very hypervisor-specific, > but XNU and FreeBSD as guests will look for 0x4000_0010 unconditionally, > under any hypervisor. The EC2 Nitro hypervisor has also exposed TSC > frequency information in this leaf, since 2020. > > As things stand, KVM guests have to reverse-calculate the TSC frequency > from the mul/shift information given to them in the KVM clock to convert > ticks into nanoseconds, with a corresponding loss of precision. I would rather have the VMM use the Intel-define CPUID.0x15 to enumerate the TSC frequency. I would also love, love, love reviews on that series. https://lore.kernel.org/all/20250227021855.3257188-36-seanjc@xxxxxxxxxx
