Currently, the kernel permits userspace VMMs to enable and use the
VMX-preemption timer by allowing writes to the following VMCS fields:
- VMX_GUEST_PREEMPTION_TIMER_VALUE (count)
- VMX_CONTROL_PIN_EXECUTION_CONTROLS (timer enable bit)
- VMX_CONTROL_EXIT_CONTROLS (save current count on context switch bit)
It also forwards the timer expiry event as a VM exit.
But it does not tell userspace how fast the timer will count down,
making it impossible to use. This commit exposes the timer's scale
via `seL4_X86_VCPU_ReadMSR`.
Signed-off-by: Bill Nguyen <bill.nguyen@unsw.edu.au>
744104654d