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 0x40000010 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. There's certainly no way we can sanely use 0x4000_0010 for anything *else* at this point. Just adopt it, as both guest and host. We already have the infrastructure for keeping the TSC frequency information up to date for the Xen CPUID leaf anyway, so do precisely the same for this one. David Woodhouse (3): KVM: x86: Restore caching of KVM CPUID base KVM: x86: Provide TSC frequency in "generic" timing infomation CPUID leaf x86/kvm: Obtain TSC frequency from CPUID if present arch/x86/include/asm/kvm_host.h | 1 + arch/x86/include/asm/kvm_para.h | 1 + arch/x86/include/uapi/asm/kvm_para.h | 11 +++++++++++ arch/x86/kernel/kvm.c | 10 ++++++++++ arch/x86/kernel/kvmclock.c | 7 ++++++- arch/x86/kvm/cpuid.c | 23 ++++++++++++++++++----- 6 files changed, 47 insertions(+), 6 deletions(-)
