#define PrintDebug(fmt, args...)
#endif
+/* Overview
+ *
+ * Time handling in VMMs is challenging, and Palacios uses the highest
+ * resolution, lowest overhead timer on modern CPUs that it can - the
+ * processor timestamp counter (TSC). Note that on somewhat old processors
+ * this can be problematic; in particular, older AMD processors did not
+ * have a constant rate timestamp counter in the face of power management
+ * events. However, the latest Intel and AMD CPUs all do (should...) have a
+ * constant rate TSC, and Palacios relies on this fact.
+ *
+ * Basically, Palacios keeps track of three quantities as it runs to manage
+ * 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
+ * (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.
+ *
+ * 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).
+ *
+ *
+ *
+ */
+
+
static int handle_cpufreq_hcall(struct guest_info * info, uint_t hcall_id, void * priv_data) {
struct vm_time * time_state = &(info->time_state);
- info->vm_regs.rbx = time_state->cpu_freq;
+ info->vm_regs.rbx = time_state->guest_cpu_freq;
PrintDebug("Guest request cpu frequency: return %ld\n", (long)info->vm_regs.rbx);
-void v3_init_time(struct guest_info * info) {
- struct vm_time * time_state = &(info->time_state);
-
- time_state->cpu_freq = V3_CPU_KHZ();
-
- time_state->pause_time = 0;
- time_state->last_update = 0;
- time_state->host_offset = 0;
-
- INIT_LIST_HEAD(&(time_state->timers));
- time_state->num_timers = 0;
-
- v3_register_hypercall(info->vm_info, TIME_CPUFREQ_HCALL, handle_cpufreq_hcall, NULL);
-}
-
int v3_start_time(struct guest_info * info) {
/* We start running with guest_time == host_time */
uint64_t t = v3_get_host_time(&info->time_state);
PrintDebug("Starting initial guest time as %llu\n", t);
info->time_state.last_update = t;
- info->time_state.pause_time = t;
+ info->time_state.initial_time = t;
+ info->yield_start_cycle = t;
return 0;
}
-int v3_pause_time(struct guest_info * info) {
- V3_ASSERT(info->time_state.pause_time == 0);
- info->time_state.pause_time = v3_get_guest_time(&info->time_state);
- PrintDebug("Time paused at guest time as %llu\n",
- info->time_state.pause_time);
- return 0;
-}
-
-int v3_resume_time(struct guest_info * info) {
- uint64_t t = v3_get_host_time(&info->time_state);
- V3_ASSERT(info->time_state.pause_time != 0);
- info->time_state.host_offset =
- (sint64_t)info->time_state.pause_time - (sint64_t)t;
-#ifdef CONFIG_TIME_TSC_OFFSET_ADJUST
- /* XXX Adjust host_offset towards zero based on resolution/accuracy
- * constraints. */
-#endif
- info->time_state.pause_time = 0;
- PrintDebug("Time resumed paused at guest time as %llu "
- "offset %lld from host time.\n", t, info->time_state.host_offset);
+// If the guest is supposed to run slower than the host, yield out until
+// the host time is appropriately far along;
+int v3_adjust_time(struct guest_info * info) {
+ struct vm_time * time_state = &(info->time_state);
+ if (time_state->host_cpu_freq == time_state->guest_cpu_freq) {
+ time_state->guest_host_offset = 0;
+ } else {
+ uint64_t guest_time, host_time, target_host_time;
+ guest_time = v3_get_guest_time(time_state);
+ host_time = v3_get_host_time(time_state);
+ target_host_time = (host_time - time_state->initial_time) *
+ time_state->host_cpu_freq / time_state->guest_cpu_freq;
+ while (host_time < target_host_time) {
+ v3_yield(info);
+ host_time = v3_get_host_time(time_state);
+ }
+ time_state->guest_host_offset = guest_time - host_time;
+ }
return 0;
}
return 0;
}
-
int v3_remove_timer(struct guest_info * info, struct vm_timer * timer) {
list_del(&(timer->timer_link));
info->time_state.num_timers--;
cycles = info->time_state.last_update - old_time;
list_for_each_entry(tmp_timer, &(info->time_state.timers), timer_link) {
- tmp_timer->ops->update_timer(info, cycles, info->time_state.cpu_freq, tmp_timer->private_data);
+ tmp_timer->ops->update_timer(info, cycles, info->time_state.guest_cpu_freq, tmp_timer->private_data);
}
}
+
+/*
+ * 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.
+ */
+
+int v3_rdtsc(struct guest_info * info) {
+ uint64_t tscval = v3_get_guest_tsc(&info->time_state);
+ info->vm_regs.rdx = tscval >> 32;
+ info->vm_regs.rax = tscval & 0xffffffffLL;
+ return 0;
+}
+
+int v3_handle_rdtsc(struct guest_info * info) {
+ v3_rdtsc(info);
+
+ info->vm_regs.rax &= 0x00000000ffffffffLL;
+ info->vm_regs.rdx &= 0x00000000ffffffffLL;
+
+ info->rip += 2;
+
+ return 0;
+}
+
+int v3_rdtscp(struct guest_info * info) {
+ int ret;
+ /* First get the MSR value that we need. It's safe to futz with
+ * ra/c/dx here since they're modified by this instruction anyway. */
+ info->vm_regs.rcx = TSC_AUX_MSR;
+ ret = v3_handle_msr_read(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 */
+ ret = v3_rdtsc(info);
+ if (ret) return ret;
+
+ return 0;
+}
+
+
+int v3_handle_rdtscp(struct guest_info * info) {
+
+ v3_rdtscp(info);
+
+ info->vm_regs.rax &= 0x00000000ffffffffLL;
+ info->vm_regs.rcx &= 0x00000000ffffffffLL;
+ info->vm_regs.rdx &= 0x00000000ffffffffLL;
+
+ info->rip += 3;
+
+ return 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);
+
+ V3_ASSERT(msr_num == TSC_AUX_MSR);
+ msr_val->lo = time_state->tsc_aux.lo;
+ msr_val->hi = time_state->tsc_aux.hi;
+
+ return 0;
+}
+
+static int tsc_aux_msr_write_hook(struct guest_info *info, uint_t msr_num,
+ struct v3_msr msr_val, void *priv) {
+ struct vm_time * time_state = &(info->time_state);
+
+ V3_ASSERT(msr_num == TSC_AUX_MSR);
+ time_state->tsc_aux.lo = msr_val.lo;
+ time_state->tsc_aux.hi = msr_val.hi;
+
+ return 0;
+}
+
+static int tsc_msr_read_hook(struct guest_info *info, uint_t msr_num,
+ struct v3_msr *msr_val, void *priv) {
+ uint64_t time = v3_get_guest_tsc(&info->time_state);
+
+ V3_ASSERT(msr_num == TSC_MSR);
+ msr_val->hi = time >> 32;
+ msr_val->lo = time & 0xffffffffLL;
+
+ return 0;
+}
+
+static int tsc_msr_write_hook(struct guest_info *info, uint_t msr_num,
+ struct v3_msr msr_val, void *priv) {
+ struct vm_time * time_state = &(info->time_state);
+ uint64_t guest_time, new_tsc;
+ V3_ASSERT(msr_num == TSC_MSR);
+ new_tsc = (((uint64_t)msr_val.hi) << 32) | (uint64_t)msr_val.lo;
+ guest_time = v3_get_guest_time(time_state);
+ time_state->tsc_guest_offset = (sint64_t)new_tsc - (sint64_t)guest_time;
+
+ return 0;
+}
+
+static int init_vm_time(struct v3_vm_info *vm_info) {
+ int ret;
+
+ PrintDebug("Installing TSC MSR hook.\n");
+ ret = v3_hook_msr(vm_info, TSC_MSR,
+ tsc_msr_read_hook, tsc_msr_write_hook, NULL);
+
+ PrintDebug("Installing TSC_AUX MSR hook.\n");
+ if (ret) return ret;
+ ret = v3_hook_msr(vm_info, TSC_AUX_MSR, tsc_aux_msr_read_hook,
+ tsc_aux_msr_write_hook, NULL);
+ if (ret) return ret;
+
+ PrintDebug("Registering TIME_CPUFREQ hypercall.\n");
+ ret = v3_register_hypercall(vm_info, TIME_CPUFREQ_HCALL,
+ handle_cpufreq_hcall, NULL);
+ return ret;
+}
+
+void v3_init_time(struct guest_info * info) {
+ struct vm_time * time_state = &(info->time_state);
+ static int one_time = 0;
+
+ time_state->host_cpu_freq = V3_CPU_KHZ();
+ time_state->guest_cpu_freq = V3_CPU_KHZ();
+
+ time_state->initial_time = 0;
+ time_state->last_update = 0;
+ time_state->guest_host_offset = 0;
+ time_state->tsc_guest_offset = 0;
+
+ INIT_LIST_HEAD(&(time_state->timers));
+ time_state->num_timers = 0;
+
+ time_state->tsc_aux.lo = 0;
+ time_state->tsc_aux.hi = 0;
+
+ if (!one_time) {
+ init_vm_time(info->vm_info);
+ one_time = 1;
+ }
+}
+
+
+
+
+
+
