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_time.h>
22 #include <palacios/vmm.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);
89 #ifdef CONFIG_TIME_HIDE_VM_COST
90 info->time_state.pause_time = t;
92 info->time_state.pause_time = 0;
94 info->time_state.last_update = t;
95 info->time_state.initial_time = t;
96 info->yield_start_cycle = t;
100 // If the guest is supposed to run slower than the host, yield out until
101 // the host time is appropriately far along;
102 int v3_adjust_time(struct guest_info * info) {
103 struct vm_time * time_state = &(info->time_state);
105 if (time_state->host_cpu_freq != time_state->guest_cpu_freq) {
106 uint64_t guest_time, guest_elapsed, desired_elapsed;
107 uint64_t host_time, target_host_time;
109 guest_time = v3_get_guest_time(time_state);
111 /* Compute what host time this guest time should correspond to. */
112 guest_elapsed = (guest_time - time_state->initial_time);
113 desired_elapsed = (guest_elapsed * time_state->host_cpu_freq) / time_state->guest_cpu_freq;
114 target_host_time = time_state->initial_time + desired_elapsed;
116 /* Yield until that host time is reached */
117 host_time = v3_get_host_time(time_state);
119 while (host_time < target_host_time) {
121 host_time = v3_get_host_time(time_state);
124 // This overrides any pause/unpause times because the difference
125 // is going to be too big for any pause/unpause the notice.
126 time_state->guest_host_offset = (sint64_t)guest_time - (sint64_t)host_time;
133 v3_pause_time( struct guest_info * info )
135 struct vm_time * time_state = &(info->time_state);
136 if (time_state->pause_time == 0) {
137 time_state->pause_time = v3_get_host_time(time_state);
138 // PrintDebug("Pausing at host time %llu.\n", time_state->pause_time);
140 PrintError("Palacios timekeeping paused when already paused.\n");
146 v3_restart_time( struct guest_info * info )
148 struct vm_time * time_state = &(info->time_state);
150 if (time_state->pause_time) {
151 sint64_t pause_diff = (v3_get_host_time(time_state) - time_state->pause_time);
152 time_state->guest_host_offset -= pause_diff;
153 time_state->pause_time = 0;
154 // PrintDebug("Resuming time after %lld cycles with offset %lld.\n", pause_diff, time_state->guest_host_offset);
156 PrintError( "Palacios time keeping restarted when not paused.");
162 int v3_offset_time( struct guest_info * info, sint64_t offset )
164 struct vm_time * time_state = &(info->time_state);
165 // PrintDebug("Adding additional offset of %lld to guest time.\n", offset);
166 time_state->guest_host_offset += offset;
170 struct v3_timer * v3_add_timer(struct guest_info * info,
171 struct v3_timer_ops * ops,
172 void * private_data) {
173 struct v3_timer * timer = NULL;
174 timer = (struct v3_timer *)V3_Malloc(sizeof(struct v3_timer));
175 V3_ASSERT(timer != NULL);
178 timer->private_data = private_data;
180 list_add(&(timer->timer_link), &(info->time_state.timers));
181 info->time_state.num_timers++;
186 int v3_remove_timer(struct guest_info * info, struct v3_timer * timer) {
187 list_del(&(timer->timer_link));
188 info->time_state.num_timers--;
194 void v3_update_timers(struct guest_info * info) {
195 struct vm_time *time_state = &info->time_state;
196 struct v3_timer * tmp_timer;
197 uint64_t old_time = info->time_state.last_update;
200 time_state->last_update = v3_get_guest_time(time_state);
201 cycles = time_state->last_update - old_time;
203 // PrintDebug("Updating timer for %lld elapsed cycles (pt=%llu, offset=%lld).\n",
204 // cycles, time_state->pause_time, time_state->guest_host_offset);
206 list_for_each_entry(tmp_timer, &(time_state->timers), timer_link) {
207 tmp_timer->ops->update_timer(info, cycles, time_state->guest_cpu_freq, tmp_timer->private_data);
212 * Handle full virtualization of the time stamp counter. As noted
213 * above, we don't store the actual value of the TSC, only the guest's
214 * offset from monotonic guest's time. If the guest writes to the TSC, we
215 * handle this by changing that offset.
217 * Possible TODO: Proper hooking of TSC read/writes?
220 int v3_rdtsc(struct guest_info * info) {
221 uint64_t tscval = v3_get_guest_tsc(&info->time_state);
222 PrintDebug("Returning %llu as TSC.\n", tscval);
223 info->vm_regs.rdx = tscval >> 32;
224 info->vm_regs.rax = tscval & 0xffffffffLL;
228 int v3_handle_rdtsc(struct guest_info * info) {
229 PrintDebug("Handling virtual RDTSC call.\n");
232 info->vm_regs.rax &= 0x00000000ffffffffLL;
233 info->vm_regs.rdx &= 0x00000000ffffffffLL;
240 int v3_rdtscp(struct guest_info * info) {
242 /* First get the MSR value that we need. It's safe to futz with
243 * ra/c/dx here since they're modified by this instruction anyway. */
244 info->vm_regs.rcx = TSC_AUX_MSR;
245 ret = v3_handle_msr_read(info);
251 info->vm_regs.rcx = info->vm_regs.rax;
253 /* Now do the TSC half of the instruction */
254 ret = v3_rdtsc(info);
264 int v3_handle_rdtscp(struct guest_info * info) {
265 PrintDebug("Handling virtual RDTSCP call.\n");
269 info->vm_regs.rax &= 0x00000000ffffffffLL;
270 info->vm_regs.rcx &= 0x00000000ffffffffLL;
271 info->vm_regs.rdx &= 0x00000000ffffffffLL;
278 static int tsc_aux_msr_read_hook(struct guest_info *info, uint_t msr_num,
279 struct v3_msr *msr_val, void *priv) {
280 struct vm_time * time_state = &(info->time_state);
282 V3_ASSERT(msr_num == TSC_AUX_MSR);
284 msr_val->lo = time_state->tsc_aux.lo;
285 msr_val->hi = time_state->tsc_aux.hi;
290 static int tsc_aux_msr_write_hook(struct guest_info *info, uint_t msr_num,
291 struct v3_msr msr_val, void *priv) {
292 struct vm_time * time_state = &(info->time_state);
294 V3_ASSERT(msr_num == TSC_AUX_MSR);
296 time_state->tsc_aux.lo = msr_val.lo;
297 time_state->tsc_aux.hi = msr_val.hi;
302 static int tsc_msr_read_hook(struct guest_info *info, uint_t msr_num,
303 struct v3_msr *msr_val, void *priv) {
304 uint64_t time = v3_get_guest_tsc(&info->time_state);
306 V3_ASSERT(msr_num == TSC_MSR);
308 msr_val->hi = time >> 32;
309 msr_val->lo = time & 0xffffffffLL;
314 static int tsc_msr_write_hook(struct guest_info *info, uint_t msr_num,
315 struct v3_msr msr_val, void *priv) {
316 struct vm_time * time_state = &(info->time_state);
317 uint64_t guest_time, new_tsc;
319 V3_ASSERT(msr_num == TSC_MSR);
321 new_tsc = (((uint64_t)msr_val.hi) << 32) | (uint64_t)msr_val.lo;
322 guest_time = v3_get_guest_time(time_state);
323 time_state->tsc_guest_offset = (sint64_t)new_tsc - (sint64_t)guest_time;
329 int v3_init_time_vm(struct v3_vm_info * vm) {
332 PrintDebug("Installing TSC MSR hook.\n");
333 ret = v3_hook_msr(vm, TSC_MSR,
334 tsc_msr_read_hook, tsc_msr_write_hook, NULL);
340 PrintDebug("Installing TSC_AUX MSR hook.\n");
341 ret = v3_hook_msr(vm, TSC_AUX_MSR, tsc_aux_msr_read_hook,
342 tsc_aux_msr_write_hook, NULL);
348 PrintDebug("Registering TIME_CPUFREQ hypercall.\n");
349 ret = v3_register_hypercall(vm, TIME_CPUFREQ_HCALL,
350 handle_cpufreq_hcall, NULL);
355 void v3_deinit_time_vm(struct v3_vm_info * vm) {
356 v3_unhook_msr(vm, TSC_MSR);
357 v3_unhook_msr(vm, TSC_AUX_MSR);
359 v3_remove_hypercall(vm, TIME_CPUFREQ_HCALL);
362 void v3_init_time_core(struct guest_info * info) {
363 struct vm_time * time_state = &(info->time_state);
364 v3_cfg_tree_t * cfg_tree = info->core_cfg_data;
367 time_state->host_cpu_freq = V3_CPU_KHZ();
368 khz = v3_cfg_val(cfg_tree, "khz");
371 time_state->guest_cpu_freq = atoi(khz);
372 PrintDebug("Core %d CPU frequency requested at %d khz.\n",
373 info->cpu_id, time_state->guest_cpu_freq);
376 if ((khz == NULL) || (time_state->guest_cpu_freq > time_state->host_cpu_freq)) {
377 time_state->guest_cpu_freq = time_state->host_cpu_freq;
380 PrintDebug("Core %d CPU frequency set to %d KHz (host CPU frequency = %d KHz).\n",
382 time_state->guest_cpu_freq,
383 time_state->host_cpu_freq);
385 time_state->initial_time = 0;
386 time_state->last_update = 0;
387 time_state->guest_host_offset = 0;
388 time_state->tsc_guest_offset = 0;
390 INIT_LIST_HEAD(&(time_state->timers));
391 time_state->num_timers = 0;
393 time_state->tsc_aux.lo = 0;
394 time_state->tsc_aux.hi = 0;
400 void v3_deinit_time_core(struct guest_info * core) {
401 struct vm_time * time_state = &(core->time_state);
402 struct v3_timer * tmr = NULL;
403 struct v3_timer * tmp = NULL;
405 list_for_each_entry_safe(tmr, tmp, &(time_state->timers), timer_link) {
406 v3_remove_timer(core, tmr);