no_timer_check is added implicitly when the kernel detects it is booting under KVM.
However when booting under TCG (software emulation) you have to add this to the guest kernel command line explicitly.
TBH I believe this is a bug: the kernel should add this flag automatically whenever it detects any kind of virtualization being used, but it doesn't right now so you have to add it.
Just a note:
no_timer_check is added implicitly when the kernel detects it is booting under KVM.
However when booting under TCG (software emulation) you have to add this to the guest kernel command line explicitly.
TBH I believe this is a bug: the kernel should add this flag automatically whenever it detects any kind of virtualization being used, but it doesn't right now so you have to add it.