* the passage of time:
* (1) The host timestamp counter - read directly from HW and never written
* (2) A monotonic guest timestamp counter used to measure the progression of
- * time in the guest. This is computed as a multipler/offset from (1) above
+ * time in the guest. This is computed using an offsets from (1) above.
* (3) The actual guest timestamp counter (which can be written by
* writing to the guest TSC MSR - MSR 0x10) from the monotonic guest TSC.
* This is also computed as an offset from (2) above when the TSC and
* this offset is updated when the TSC MSR is written.
*
+ * The value used to offset the guest TSC from the host TSC is the *sum* of all
+ * of these offsets (2 and 3) above
+ *
* Because all other devices are slaved off of the passage of time in the guest,
* it is (2) above that drives the firing of other timers in the guest,
* including timer devices such as the Programmable Interrupt Timer (PIT).
*
- *
- *
+ * Future additions:
+ * (1) Add support for temporarily skewing guest time off of where it should
+ * be to support slack simulation of guests. The idea is that simulators
+ * set this skew to be the difference between how much time passed for a
+ * simulated feature and a real implementation of that feature, making
+ * pass at a different rate from real time on this core. The VMM will then
+ * attempt to move this skew back towards 0 subject to resolution/accuracy
+ * constraints from various system timers.
+ *
+ * The main effort in doing this will be to get accuracy/resolution
+ * information from each local timer and to use this to bound how much skew
+ * is removed on each exit.
*/
} else {
uint64_t guest_time, guest_elapsed, desired_elapsed;
uint64_t host_time, target_host_time;
+
guest_time = v3_get_guest_time(time_state);
+
+ /* Compute what host time this guest time should correspond to. */
guest_elapsed = (guest_time - time_state->initial_time);
desired_elapsed = (guest_elapsed * time_state->host_cpu_freq) / time_state->guest_cpu_freq;
-
target_host_time = time_state->initial_time + desired_elapsed;
- host_time = v3_get_host_time(time_state);
- PrintDebug("Core %d: Yielding %Lu cycles for guest frequency mismatch "
- "(%Lu cycles elapsed in guest, %Lu in host).\n",
- info->cpu_id, target_host_time - host_time,
- guest_elapsed, host_time - time_state->initial_time);
+ /* Yield until that host time is reached */
host_time = v3_get_host_time(time_state);
while (host_time < target_host_time) {
v3_yield(info);
host_time = v3_get_host_time(time_state);
}
- PrintDebug("Core %d: done adjusting time at host time %Lu.\n",
- info->cpu_id, host_time);
- time_state->guest_host_offset = guest_time - host_time;
-
+ time_state->guest_host_offset = (sint64_t)guest_time - (sint64_t)host_time;
}
return 0;
}
-int v3_add_timer(struct guest_info * info, struct vm_timer_ops * ops,
- void * private_data) {
- struct vm_timer * timer = NULL;
- timer = (struct vm_timer *)V3_Malloc(sizeof(struct vm_timer));
+struct v3_timer * v3_add_timer(struct guest_info * info,
+ struct v3_timer_ops * ops,
+ void * private_data) {
+ struct v3_timer * timer = NULL;
+ timer = (struct v3_timer *)V3_Malloc(sizeof(struct v3_timer));
V3_ASSERT(timer != NULL);
timer->ops = ops;
list_add(&(timer->timer_link), &(info->time_state.timers));
info->time_state.num_timers++;
- return 0;
+ return timer;
}
-int v3_remove_timer(struct guest_info * info, struct vm_timer * timer) {
+int v3_remove_timer(struct guest_info * info, struct v3_timer * timer) {
list_del(&(timer->timer_link));
info->time_state.num_timers--;
}
void v3_update_timers(struct guest_info * info) {
- struct vm_timer * tmp_timer;
+ struct v3_timer * tmp_timer;
uint64_t old_time = info->time_state.last_update;
uint64_t cycles;
/*
* Handle full virtualization of the time stamp counter. As noted
* above, we don't store the actual value of the TSC, only the guest's
- * offset from the host TSC. If the guest write's the to TSC, we handle
- * this by changing that offset.
+ * offset from monotonic guest's time. If the guest writes to the TSC, we
+ * handle this by changing that offset.
+ *
+ * Possible TODO: Proper hooking of TSC read/writes?
*/
int v3_rdtsc(struct guest_info * info) {
if (ret) return ret;
info->vm_regs.rcx = info->vm_regs.rax;
- /* Now do the TSC half of the instruction, which may hit the normal
- * TSC hook if it exists */
+ /* Now do the TSC half of the instruction */
ret = v3_rdtsc(info);
if (ret) return ret;
return 0;
}
-#if 0
static int tsc_aux_msr_read_hook(struct guest_info *info, uint_t msr_num,
struct v3_msr *msr_val, void *priv) {
struct vm_time * time_state = &(info->time_state);
return 0;
}
-#endif
static int init_vm_time(struct v3_vm_info *vm_info) {
int ret;
-#if 0
PrintDebug("Installing TSC MSR hook.\n");
ret = v3_hook_msr(vm_info, TSC_MSR,
tsc_msr_read_hook, tsc_msr_write_hook, NULL);
ret = v3_hook_msr(vm_info, TSC_AUX_MSR, tsc_aux_msr_read_hook,
tsc_aux_msr_write_hook, NULL);
if (ret) return ret;
-#endif
PrintDebug("Registering TIME_CPUFREQ hypercall.\n");
ret = v3_register_hypercall(vm_info, TIME_CPUFREQ_HCALL,
+
+
+
