2 * This file is part of the Palacios Virtual Machine Monitor developed
3 * by the V3VEE Project with funding from the United States National
4 * Science Foundation and the Department of Energy.
6 * The V3VEE Project is a joint project between Northwestern University
7 * and the University of New Mexico. You can find out more at
10 * Copyright (c) 2008, Jack Lange <jarusl@cs.northwestern.edu>
11 * Copyright (c) 2008, The V3VEE Project <http://www.v3vee.org>
12 * All rights reserved.
14 * Author: Jack Lange <jarusl@cs.northwestern.edu>
15 * Patrick G. Bridges <bridges@cs.unm.edu>
17 * This is free software. You are permitted to use,
18 * redistribute, and modify it as specified in the file "V3VEE_LICENSE".
21 #include <palacios/vmm.h>
22 #include <palacios/vmm_time.h>
23 #include <palacios/vm_guest.h>
25 #ifndef V3_CONFIG_DEBUG_TIME
27 #define PrintDebug(fmt, args...)
32 * Time handling in VMMs is challenging, and Palacios uses the highest
33 * resolution, lowest overhead timer on modern CPUs that it can - the
34 * processor timestamp counter (TSC). Note that on somewhat old processors
35 * this can be problematic; in particular, older AMD processors did not
36 * have a constant rate timestamp counter in the face of power management
37 * events. However, the latest Intel and AMD CPUs all do (should...) have a
38 * constant rate TSC, and Palacios relies on this fact.
40 * Basically, Palacios keeps track of three quantities as it runs to manage
41 * the passage of time:
42 * (1) The host timestamp counter - read directly from HW and never written
43 * (2) A monotonic guest timestamp counter used to measure the progression of
44 * time in the guest. This is stored as an absolute number of cycles elapsed
45 * and is updated on guest entry and exit; it can also be updated explicitly
46 * in the monitor at times
47 * (3) The actual guest timestamp counter (which can be written by
48 * writing to the guest TSC MSR - MSR 0x10) from the monotonic guest TSC.
49 * This is also computed as an offset from (2) above when the TSC and
50 * this offset is updated when the TSC MSR is written.
52 * Because all other devices are slaved off of the passage of time in the guest,
53 * it is (2) above that drives the firing of other timers in the guest,
54 * including timer devices such as the Programmable Interrupt Timer (PIT).
57 * (1) Add support for temporarily skewing guest time off of where it should
58 * be to support slack simulation of guests. The idea is that simulators
59 * set this skew to be the difference between how much time passed for a
60 * simulated feature and a real implementation of that feature, making time
61 * pass at a different rate from real time on this core. The VMM will then
62 * attempt to move this skew back towards 0 subject to resolution/accuracy
63 * constraints from various system timers.
65 * The main effort in doing this will be to get accuracy/resolution
66 * information from each local timer and to use this to bound how much skew
67 * is removed on each exit.
69 * (2) Look more into sychronizing the offsets *across* virtual and physical
70 * cores so that multicore guests stay mostly in sync.
72 * (3) Look into using the AMD TSC multiplier feature and adding explicit time
73 * dilation support to time handling.
77 static int handle_cpufreq_hcall(struct guest_info * info, uint_t hcall_id, void * priv_data) {
78 struct vm_core_time * time_state = &(info->time_state);
80 info->vm_regs.rbx = time_state->guest_cpu_freq;
82 PrintDebug("Guest request cpu frequency: return %ld\n", (long)info->vm_regs.rbx);
89 int v3_start_time(struct guest_info * info) {
90 /* We start running with guest_time == host_time */
91 uint64_t t = v3_get_host_time(&info->time_state);
93 info->time_state.enter_time = 0;
94 info->time_state.exit_time = t;
95 info->time_state.initial_time = t;
96 info->yield_start_cycle = t;
98 info->time_state.last_update = 0;
99 info->time_state.guest_cycles = 0;
100 PrintDebug("Starting time for core %d at host time %llu/guest time %llu.\n",
101 info->vcpu_id, t, info->time_state.guest_cycles);
106 int v3_offset_time( struct guest_info * info, sint64_t offset )
108 struct vm_core_time * time_state = &(info->time_state);
109 PrintDebug("Adding additional offset of %lld to guest time.\n", offset);
110 time_state->guest_cycles += offset;
114 #ifdef V3_CONFIG_TIME_DILATION
115 static uint64_t compute_target_host_time(struct guest_info * info, uint64_t guest_time)
117 struct vm_core_time * time_state = &(info->time_state);
118 uint64_t guest_elapsed, desired_elapsed;
120 guest_elapsed = (guest_time - time_state->initial_time);
121 desired_elapsed = (guest_elapsed * time_state->host_cpu_freq) / time_state->guest_cpu_freq;
122 return time_state->initial_time + desired_elapsed;
125 static uint64_t compute_target_guest_time(struct guest_info *info)
127 struct vm_core_time * time_state = &(info->time_state);
128 uint64_t host_elapsed, desired_elapsed;
130 host_elapsed = v3_get_host_time(time_state) - time_state->initial_time;
131 desired_elapsed = (host_elapsed * time_state->guest_cpu_freq) / time_state->host_cpu_freq;
133 return time_state->initial_time + desired_elapsed;
137 /* Yield time in the host to deal with a guest that wants to run slower than
138 * the native host cycle frequency */
139 static int yield_host_time(struct guest_info * info) {
140 struct vm_core_time * time_state = &(info->time_state);
141 uint64_t host_time, target_host_time;
142 uint64_t guest_time, old_guest_time;
144 /* Now, let the host run while the guest is stopped to make the two
145 * sync up. Note that this doesn't assume that guest time is stopped;
146 * the offsetting in the next step will change add an offset to guest
147 * time to account for the time paused even if the geust isn't
148 * usually paused in the VMM. */
149 host_time = v3_get_host_time(time_state);
150 old_guest_time = v3_get_guest_time(time_state);
151 target_host_time = compute_target_host_time(info, old_guest_time);
153 while (target_host_time > host_time) {
155 host_time = v3_get_host_time(time_state);
158 guest_time = v3_get_guest_time(time_state);
160 /* We do *not* assume the guest timer was paused in the VM. If it was
161 * this offseting is 0. If it wasn't, we need this. */
162 v3_offset_time(info, (sint64_t)(old_guest_time - guest_time));
167 static int skew_guest_time(struct guest_info * info) {
168 struct vm_core_time * time_state = &(info->time_state);
169 uint64_t target_guest_time, guest_time;
170 /* Now the host may have gotten ahead of the guest because
171 * yielding is a coarse grained thing. Figure out what guest time
172 * we want to be at, and use the use the offsetting mechanism in
173 * the VMM to make the guest run forward. We limit *how* much we skew
174 * it forward to prevent the guest time making large jumps,
176 target_guest_time = compute_target_guest_time(info);
177 guest_time = v3_get_guest_time(time_state);
179 if (guest_time < target_guest_time) {
180 sint64_t max_skew, desired_skew, skew;
182 if (time_state->enter_time) {
183 /* Limit forward skew to 10% of the amount the guest has
184 * run since we last could skew time */
185 max_skew = (sint64_t)(guest_time - time_state->enter_time) / 10;
190 desired_skew = (sint64_t)(target_guest_time - guest_time);
191 skew = desired_skew > max_skew ? max_skew : desired_skew;
192 PrintDebug("Guest %lld cycles behind where it should be.\n",
194 PrintDebug("Limit on forward skew is %lld. Skewing forward %lld.\n",
197 v3_offset_time(info, skew);
202 #endif /* V3_CONFIG_TIME_DILATION */
204 // Control guest time in relation to host time so that the two stay
205 // appropriately synchronized to the extent possible.
206 int v3_adjust_time(struct guest_info * info) {
208 #ifdef V3_CONFIG_TIME_DILATION
209 /* First deal with yielding if we want to slow down the guest */
210 yield_host_time(info);
212 /* Now, if the guest is too slow, (either from excess yielding above,
213 * or because the VMM is doing something that takes a long time to emulate)
214 * allow guest time to jump forward a bit */
215 skew_guest_time(info);
220 /* Called immediately upon entry in the the VMM */
222 v3_time_exit_vm( struct guest_info * info, uint64_t * guest_cycles )
224 struct vm_core_time * time_state = &(info->time_state);
226 time_state->exit_time = v3_get_host_time(time_state);
228 time_state->guest_cycles += *guest_cycles;
230 uint64_t cycles_exec;
231 cycles_exec = time_state->exit_time - time_state->enter_time;
232 time_state->guest_cycles += cycles_exec;
237 /* Called immediately prior to entry to the VM */
239 v3_time_enter_vm( struct guest_info * info )
241 struct vm_core_time * time_state = &(info->time_state);
242 uint64_t host_time, vmm_cycles;
244 host_time = v3_get_host_time(time_state);
245 time_state->enter_time = host_time;
246 vmm_cycles = host_time - time_state->exit_time;
247 /* XXX How do we want to take into account host/guest CPU speed differences
248 * and time dilation here? Probably time just won't advance in the VMM in that
249 * case so its irrelvant XXX */
250 time_state->guest_cycles += vmm_cycles;
256 struct v3_timer * v3_add_timer(struct guest_info * info,
257 struct v3_timer_ops * ops,
258 void * private_data) {
259 struct v3_timer * timer = NULL;
260 timer = (struct v3_timer *)V3_Malloc(sizeof(struct v3_timer));
261 V3_ASSERT(timer != NULL);
264 timer->private_data = private_data;
266 list_add(&(timer->timer_link), &(info->time_state.timers));
267 info->time_state.num_timers++;
272 int v3_remove_timer(struct guest_info * info, struct v3_timer * timer) {
273 list_del(&(timer->timer_link));
274 info->time_state.num_timers--;
280 void v3_update_timers(struct guest_info * info) {
281 struct vm_core_time *time_state = &info->time_state;
282 struct v3_timer * tmp_timer;
284 uint64_t old_time = info->time_state.last_update;
286 time_state->last_update = v3_get_guest_time(time_state);
287 cycles = (sint64_t)(time_state->last_update - old_time);
288 V3_ASSERT(cycles >= 0);
290 // V3_Print("Updating timers with %lld elapsed cycles.\n", cycles);
291 list_for_each_entry(tmp_timer, &(time_state->timers), timer_link) {
292 tmp_timer->ops->update_timer(info, cycles, time_state->guest_cpu_freq, tmp_timer->private_data);
298 * Handle full virtualization of the time stamp counter. As noted
299 * above, we don't store the actual value of the TSC, only the guest's
300 * offset from monotonic guest's time. If the guest writes to the TSC, we
301 * handle this by changing that offset.
303 * Possible TODO: Proper hooking of TSC read/writes?
306 int v3_rdtsc(struct guest_info * info) {
307 uint64_t tscval = v3_get_guest_tsc(&info->time_state);
309 info->vm_regs.rdx = tscval >> 32;
310 info->vm_regs.rax = tscval & 0xffffffffLL;
315 int v3_handle_rdtsc(struct guest_info * info) {
318 info->vm_regs.rax &= 0x00000000ffffffffLL;
319 info->vm_regs.rdx &= 0x00000000ffffffffLL;
326 int v3_rdtscp(struct guest_info * info) {
328 /* First get the MSR value that we need. It's safe to futz with
329 * ra/c/dx here since they're modified by this instruction anyway. */
330 info->vm_regs.rcx = TSC_AUX_MSR;
331 ret = v3_handle_msr_read(info);
337 info->vm_regs.rcx = info->vm_regs.rax;
339 /* Now do the TSC half of the instruction */
340 ret = v3_rdtsc(info);
350 int v3_handle_rdtscp(struct guest_info * info) {
351 PrintDebug("Handling virtual RDTSCP call.\n");
355 info->vm_regs.rax &= 0x00000000ffffffffLL;
356 info->vm_regs.rcx &= 0x00000000ffffffffLL;
357 info->vm_regs.rdx &= 0x00000000ffffffffLL;
364 static int tsc_aux_msr_read_hook(struct guest_info *info, uint_t msr_num,
365 struct v3_msr *msr_val, void *priv) {
366 struct vm_core_time * time_state = &(info->time_state);
368 V3_ASSERT(msr_num == TSC_AUX_MSR);
370 msr_val->lo = time_state->tsc_aux.lo;
371 msr_val->hi = time_state->tsc_aux.hi;
376 static int tsc_aux_msr_write_hook(struct guest_info *info, uint_t msr_num,
377 struct v3_msr msr_val, void *priv) {
378 struct vm_core_time * time_state = &(info->time_state);
380 V3_ASSERT(msr_num == TSC_AUX_MSR);
382 time_state->tsc_aux.lo = msr_val.lo;
383 time_state->tsc_aux.hi = msr_val.hi;
388 static int tsc_msr_read_hook(struct guest_info *info, uint_t msr_num,
389 struct v3_msr *msr_val, void *priv) {
390 uint64_t time = v3_get_guest_tsc(&info->time_state);
392 V3_ASSERT(msr_num == TSC_MSR);
394 msr_val->hi = time >> 32;
395 msr_val->lo = time & 0xffffffffLL;
400 static int tsc_msr_write_hook(struct guest_info *info, uint_t msr_num,
401 struct v3_msr msr_val, void *priv) {
402 struct vm_core_time * time_state = &(info->time_state);
403 uint64_t guest_time, new_tsc;
405 V3_ASSERT(msr_num == TSC_MSR);
407 new_tsc = (((uint64_t)msr_val.hi) << 32) | (uint64_t)msr_val.lo;
408 guest_time = v3_get_guest_time(time_state);
409 time_state->tsc_guest_offset = (sint64_t)new_tsc - (sint64_t)guest_time;
415 int v3_init_time_vm(struct v3_vm_info * vm) {
418 PrintDebug("Installing TSC MSR hook.\n");
419 ret = v3_hook_msr(vm, TSC_MSR,
420 tsc_msr_read_hook, tsc_msr_write_hook, NULL);
426 PrintDebug("Installing TSC_AUX MSR hook.\n");
427 ret = v3_hook_msr(vm, TSC_AUX_MSR, tsc_aux_msr_read_hook,
428 tsc_aux_msr_write_hook, NULL);
434 PrintDebug("Registering TIME_CPUFREQ hypercall.\n");
435 ret = v3_register_hypercall(vm, TIME_CPUFREQ_HCALL,
436 handle_cpufreq_hcall, NULL);
438 vm->time_state.td_mult = 1;
439 PrintDebug("Setting base time dilation factor to %d.\n", vm->time_state.td_mult);
444 void v3_deinit_time_vm(struct v3_vm_info * vm) {
445 v3_unhook_msr(vm, TSC_MSR);
446 v3_unhook_msr(vm, TSC_AUX_MSR);
448 v3_remove_hypercall(vm, TIME_CPUFREQ_HCALL);
451 void v3_init_time_core(struct guest_info * info) {
452 struct vm_core_time * time_state = &(info->time_state);
453 v3_cfg_tree_t * cfg_tree = info->core_cfg_data;
456 time_state->host_cpu_freq = V3_CPU_KHZ();
457 khz = v3_cfg_val(cfg_tree, "khz");
460 time_state->guest_cpu_freq = atoi(khz);
461 PrintDebug("Logical Core %d (vcpu=%d) CPU frequency requested at %d khz.\n",
462 info->pcpu_id, info->vcpu_id, time_state->guest_cpu_freq);
465 if ( (khz == NULL) ||
466 (time_state->guest_cpu_freq <= 0) ||
467 (time_state->guest_cpu_freq > time_state->host_cpu_freq) ) {
469 time_state->guest_cpu_freq = time_state->host_cpu_freq;
472 PrintDebug("Logical Core %d (vcpu=%d) CPU frequency set to %d KHz (host CPU frequency = %d KHz).\n",
473 info->pcpu_id, info->vcpu_id,
474 time_state->guest_cpu_freq,
475 time_state->host_cpu_freq);
477 time_state->initial_time = 0;
478 time_state->last_update = 0;
479 time_state->tsc_guest_offset = 0;
480 time_state->enter_time = 0;
481 time_state->exit_time = 0;
482 time_state->guest_cycles = 0;
484 INIT_LIST_HEAD(&(time_state->timers));
485 time_state->num_timers = 0;
487 time_state->tsc_aux.lo = 0;
488 time_state->tsc_aux.hi = 0;
492 void v3_deinit_time_core(struct guest_info * core) {
493 struct vm_core_time * time_state = &(core->time_state);
494 struct v3_timer * tmr = NULL;
495 struct v3_timer * tmp = NULL;
497 list_for_each_entry_safe(tmr, tmp, &(time_state->timers), timer_link) {
498 v3_remove_timer(core, tmr);