I meant bus clock frequency, not bus lock. Sorry for typo. On Tue, Nov 07, 2023 at 11:22:32AM -0800, isaku.yamahata@xxxxxxxxx wrote: > From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx> > > Add KVM_CAP_X86_BUS_FREQUENCY_CONTROL capability to configure the core > crystal clock (or processor's bus clock) for APIC timer emulation. Allow > KVM_ENABLE_CAPABILITY(KVM_CAP_X86_BUS_FREUQNCY_CONTROL) to set the > frequency. When using this capability, the user space VMM should configure > CPUID[0x15] to advertise the frequency. > > TDX virtualizes CPUID[0x15] for the core crystal clock to be 25MHz. The > x86 KVM hardcodes its freuqncy for APIC timer to be 1GHz. This mismatch > causes the vAPIC timer to fire earlier than the guest expects. [1] The KVM > APIC timer emulation uses hrtimer, whose unit is nanosecond. > > There are options to reconcile the mismatch. 1) Make apic bus clock frequency > configurable (this patch). 2) TDX KVM code adjusts TMICT value. This is hacky > and it results in losing MSB bits from 32 bit width to 30 bit width. 3). Make > the guest kernel use tsc deadline timer instead of acpi oneshot/periodic timer. > This is guest kernel choice. It's out of control of VMM. > > [1] https://lore.kernel.org/lkml/20231006011255.4163884-1-vannapurve@xxxxxxxxxx/ > > Isaku Yamahata (2): > KVM: x86: Make the hardcoded APIC bus frequency vm variable > KVM: X86: Add a capability to configure bus frequency for APIC timer > > arch/x86/include/asm/kvm_host.h | 2 ++ > arch/x86/kvm/hyperv.c | 2 +- > arch/x86/kvm/lapic.c | 6 ++++-- > arch/x86/kvm/lapic.h | 4 ++-- > arch/x86/kvm/x86.c | 16 ++++++++++++++++ > include/uapi/linux/kvm.h | 1 + > 6 files changed, 26 insertions(+), 5 deletions(-) > > -- > 2.25.1 > -- Isaku Yamahata <isaku.yamahata@xxxxxxxxxxxxxxx>
