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 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 computed using an offsets from (1) above.
45 * (3) The actual guest timestamp counter (which can be written by
46 * writing to the guest TSC MSR - MSR 0x10) from the monotonic guest TSC.
47 * This is also computed as an offset from (2) above when the TSC and
48 * this offset is updated when the TSC MSR is written.
50 * The value used to offset the guest TSC from the host TSC is the *sum* of all
51 * of these offsets (2 and 3) above
53 * Because all other devices are slaved off of the passage of time in the guest,
54 * it is (2) above that drives the firing of other timers in the guest,
55 * including timer devices such as the Programmable Interrupt Timer (PIT).
58 * (1) Add support for temporarily skewing guest time off of where it should
59 * be to support slack simulation of guests. The idea is that simulators
60 * set this skew to be the difference between how much time passed for a
61 * simulated feature and a real implementation of that feature, making
62 * pass at a different rate from real time on this core. The VMM will then
63 * attempt to move this skew back towards 0 subject to resolution/accuracy
64 * constraints from various system timers.
66 * The main effort in doing this will be to get accuracy/resolution
67 * information from each local timer and to use this to bound how much skew
68 * is removed on each exit.
72 static int handle_cpufreq_hcall(struct guest_info * info, uint_t hcall_id, void * priv_data) {
73 struct vm_time * time_state = &(info->time_state);
75 info->vm_regs.rbx = time_state->guest_cpu_freq;
77 PrintDebug("Guest request cpu frequency: return %ld\n", (long)info->vm_regs.rbx);
84 int v3_start_time(struct guest_info * info) {
85 /* We start running with guest_time == host_time */
86 uint64_t t = v3_get_host_time(&info->time_state);
88 PrintDebug("Starting initial guest time as %llu\n", t);
90 info->time_state.enter_time = 0;
91 info->time_state.exit_time = t;
92 info->time_state.last_update = t;
93 info->time_state.initial_time = t;
94 info->yield_start_cycle = t;
99 // Control guest time in relation to host time so that the two stay
100 // appropriately synchronized to the extent possible.
101 int v3_adjust_time(struct guest_info * info) {
102 struct vm_time * time_state = &(info->time_state);
103 uint64_t host_time, target_host_time;
104 uint64_t guest_time, target_guest_time, old_guest_time;
105 uint64_t guest_elapsed, host_elapsed, desired_elapsed;
107 /* Compute the target host time given how much time has *already*
108 * passed in the guest */
109 guest_time = v3_get_guest_time(time_state);
110 guest_elapsed = (guest_time - time_state->initial_time);
111 desired_elapsed = (guest_elapsed * time_state->host_cpu_freq) / time_state->guest_cpu_freq;
112 target_host_time = time_state->initial_time + desired_elapsed;
114 /* Now, let the host run while the guest is stopped to make the two
116 host_time = v3_get_host_time(time_state);
117 old_guest_time = v3_get_guest_time(time_state);
119 while (target_host_time > host_time) {
121 host_time = v3_get_host_time(time_state);
124 guest_time = v3_get_guest_time(time_state);
126 // We do *not* assume the guest timer was paused in the VM. If it was
127 // this offseting is 0. If it wasn't we need this.
128 v3_offset_time(info, (sint64_t)old_guest_time - (sint64_t)guest_time);
130 /* Now the host may have gotten ahead of the guest because
131 * yielding is a coarse grained thing. Figure out what guest time
132 * we want to be at, and use the use the offsetting mechanism in
133 * the VMM to make the guest run forward. We limit *how* much we skew
134 * it forward to prevent the guest time making large jumps,
136 host_elapsed = host_time - time_state->initial_time;
137 desired_elapsed = (host_elapsed * time_state->guest_cpu_freq) / time_state->host_cpu_freq;
138 target_guest_time = time_state->initial_time + desired_elapsed;
140 if (guest_time < target_guest_time) {
141 uint64_t max_skew, desired_skew, skew;
143 if (time_state->enter_time) {
144 max_skew = (time_state->exit_time - time_state->enter_time) / 10;
149 desired_skew = target_guest_time - guest_time;
150 skew = desired_skew > max_skew ? max_skew : desired_skew;
151 /* PrintDebug("Guest %llu cycles behind where it should be.\n",
153 PrintDebug("Limit on forward skew is %llu. Skewing forward %llu.\n",
156 v3_offset_time(info, skew);
162 /* Called immediately upon entry in the the VMM */
164 v3_time_exit_vm( struct guest_info * info )
166 struct vm_time * time_state = &(info->time_state);
168 time_state->exit_time = v3_get_host_time(time_state);
173 /* Called immediately prior to entry to the VM */
175 v3_time_enter_vm( struct guest_info * info )
177 struct vm_time * time_state = &(info->time_state);
178 uint64_t guest_time, host_time;
180 guest_time = v3_get_guest_time(time_state);
181 host_time = v3_get_host_time(time_state);
182 time_state->enter_time = host_time;
183 time_state->guest_host_offset = guest_time - host_time;
185 // Because we just modified the offset - shouldn't matter as this should be
186 // the last time-related call prior to entering the VMM, but worth it
188 time_state->exit_time = host_time;
193 int v3_offset_time( struct guest_info * info, sint64_t offset )
195 struct vm_time * time_state = &(info->time_state);
196 // PrintDebug("Adding additional offset of %lld to guest time.\n", offset);
197 time_state->guest_host_offset += offset;
201 struct v3_timer * v3_add_timer(struct guest_info * info,
202 struct v3_timer_ops * ops,
203 void * private_data) {
204 struct v3_timer * timer = NULL;
205 timer = (struct v3_timer *)V3_Malloc(sizeof(struct v3_timer));
206 V3_ASSERT(timer != NULL);
209 timer->private_data = private_data;
211 list_add(&(timer->timer_link), &(info->time_state.timers));
212 info->time_state.num_timers++;
217 int v3_remove_timer(struct guest_info * info, struct v3_timer * timer) {
218 list_del(&(timer->timer_link));
219 info->time_state.num_timers--;
225 void v3_update_timers(struct guest_info * info) {
226 struct vm_time *time_state = &info->time_state;
227 struct v3_timer * tmp_timer;
228 uint64_t old_time = info->time_state.last_update;
231 time_state->last_update = v3_get_guest_time(time_state);
232 cycles = time_state->last_update - old_time;
234 list_for_each_entry(tmp_timer, &(time_state->timers), timer_link) {
235 tmp_timer->ops->update_timer(info, cycles, time_state->guest_cpu_freq, tmp_timer->private_data);
240 * Handle full virtualization of the time stamp counter. As noted
241 * above, we don't store the actual value of the TSC, only the guest's
242 * offset from monotonic guest's time. If the guest writes to the TSC, we
243 * handle this by changing that offset.
245 * Possible TODO: Proper hooking of TSC read/writes?
248 int v3_rdtsc(struct guest_info * info) {
249 uint64_t tscval = v3_get_guest_tsc(&info->time_state);
251 info->vm_regs.rdx = tscval >> 32;
252 info->vm_regs.rax = tscval & 0xffffffffLL;
257 int v3_handle_rdtsc(struct guest_info * info) {
260 info->vm_regs.rax &= 0x00000000ffffffffLL;
261 info->vm_regs.rdx &= 0x00000000ffffffffLL;
268 int v3_rdtscp(struct guest_info * info) {
270 /* First get the MSR value that we need. It's safe to futz with
271 * ra/c/dx here since they're modified by this instruction anyway. */
272 info->vm_regs.rcx = TSC_AUX_MSR;
273 ret = v3_handle_msr_read(info);
279 info->vm_regs.rcx = info->vm_regs.rax;
281 /* Now do the TSC half of the instruction */
282 ret = v3_rdtsc(info);
292 int v3_handle_rdtscp(struct guest_info * info) {
293 PrintDebug("Handling virtual RDTSCP call.\n");
297 info->vm_regs.rax &= 0x00000000ffffffffLL;
298 info->vm_regs.rcx &= 0x00000000ffffffffLL;
299 info->vm_regs.rdx &= 0x00000000ffffffffLL;
306 static int tsc_aux_msr_read_hook(struct guest_info *info, uint_t msr_num,
307 struct v3_msr *msr_val, void *priv) {
308 struct vm_time * time_state = &(info->time_state);
310 V3_ASSERT(msr_num == TSC_AUX_MSR);
312 msr_val->lo = time_state->tsc_aux.lo;
313 msr_val->hi = time_state->tsc_aux.hi;
318 static int tsc_aux_msr_write_hook(struct guest_info *info, uint_t msr_num,
319 struct v3_msr msr_val, void *priv) {
320 struct vm_time * time_state = &(info->time_state);
322 V3_ASSERT(msr_num == TSC_AUX_MSR);
324 time_state->tsc_aux.lo = msr_val.lo;
325 time_state->tsc_aux.hi = msr_val.hi;
330 static int tsc_msr_read_hook(struct guest_info *info, uint_t msr_num,
331 struct v3_msr *msr_val, void *priv) {
332 uint64_t time = v3_get_guest_tsc(&info->time_state);
334 V3_ASSERT(msr_num == TSC_MSR);
336 msr_val->hi = time >> 32;
337 msr_val->lo = time & 0xffffffffLL;
342 static int tsc_msr_write_hook(struct guest_info *info, uint_t msr_num,
343 struct v3_msr msr_val, void *priv) {
344 struct vm_time * time_state = &(info->time_state);
345 uint64_t guest_time, new_tsc;
347 V3_ASSERT(msr_num == TSC_MSR);
349 new_tsc = (((uint64_t)msr_val.hi) << 32) | (uint64_t)msr_val.lo;
350 guest_time = v3_get_guest_time(time_state);
351 time_state->tsc_guest_offset = (sint64_t)new_tsc - (sint64_t)guest_time;
357 int v3_init_time_vm(struct v3_vm_info * vm) {
360 PrintDebug("Installing TSC MSR hook.\n");
361 ret = v3_hook_msr(vm, TSC_MSR,
362 tsc_msr_read_hook, tsc_msr_write_hook, NULL);
368 PrintDebug("Installing TSC_AUX MSR hook.\n");
369 ret = v3_hook_msr(vm, TSC_AUX_MSR, tsc_aux_msr_read_hook,
370 tsc_aux_msr_write_hook, NULL);
376 PrintDebug("Registering TIME_CPUFREQ hypercall.\n");
377 ret = v3_register_hypercall(vm, TIME_CPUFREQ_HCALL,
378 handle_cpufreq_hcall, NULL);
383 void v3_deinit_time_vm(struct v3_vm_info * vm) {
384 v3_unhook_msr(vm, TSC_MSR);
385 v3_unhook_msr(vm, TSC_AUX_MSR);
387 v3_remove_hypercall(vm, TIME_CPUFREQ_HCALL);
390 void v3_init_time_core(struct guest_info * info) {
391 struct vm_time * time_state = &(info->time_state);
392 v3_cfg_tree_t * cfg_tree = info->core_cfg_data;
395 time_state->host_cpu_freq = V3_CPU_KHZ();
396 khz = v3_cfg_val(cfg_tree, "khz");
399 time_state->guest_cpu_freq = atoi(khz);
400 PrintDebug("Core %d CPU frequency requested at %d khz.\n",
401 info->cpu_id, time_state->guest_cpu_freq);
404 if ( (khz == NULL) ||
405 (time_state->guest_cpu_freq <= 0) ||
406 (time_state->guest_cpu_freq > time_state->host_cpu_freq) ) {
408 time_state->guest_cpu_freq = time_state->host_cpu_freq;
411 PrintDebug("Core %d CPU frequency set to %d KHz (host CPU frequency = %d KHz).\n",
413 time_state->guest_cpu_freq,
414 time_state->host_cpu_freq);
416 time_state->initial_time = 0;
417 time_state->last_update = 0;
418 time_state->guest_host_offset = 0;
419 time_state->tsc_guest_offset = 0;
421 INIT_LIST_HEAD(&(time_state->timers));
422 time_state->num_timers = 0;
424 time_state->tsc_aux.lo = 0;
425 time_state->tsc_aux.hi = 0;
429 void v3_deinit_time_core(struct guest_info * core) {
430 struct vm_time * time_state = &(core->time_state);
431 struct v3_timer * tmr = NULL;
432 struct v3_timer * tmp = NULL;
434 list_for_each_entry_safe(tmr, tmp, &(time_state->timers), timer_link) {
435 v3_remove_timer(core, tmr);