KVM_GET_SUPPORTED_CPUID must not populate guest CPUID.15H, because KVM has no way of knowing the base frequency of the local APIC emulated in userspace. However, in reality, the in-kernel APIC emulation is in prevalent use. Document how KVM_GET_SUPPORTED_CPUID would populate CPUID.15H if the in-kernel APIC were the default. Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx> --- Documentation/virt/kvm/api.rst | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index abd7c32126ce..1e09ac9d48e9 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -1786,6 +1786,16 @@ support. Instead it is reported via:: if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the feature in userspace, then you can enable the feature for KVM_SET_CPUID2. +Similarly, CPUID leaf 0x15 always returns zeroes, because the core +crystal clock frequency must match the local APIC base frequency, and +the default configuration leaves the local APIC emulation to +userspace. + +If KVM_CREATE_IRQCHIP is used to enable the in-kernel local APIC +emulation, CPUID.15H:ECX can be set to 1000000000 (0x3b9aca00). For +the default guest TSC frequency, CPUID.15H:EBX can be set to tsc_khz +and CPUID.15H:ECX can be set to 1000000 (0xf4240). The fraction can +be simplified if desired. 4.47 KVM_PPC_GET_PVINFO ----------------------- -- 2.37.3.968.ga6b4b080e4-goog
