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.initial_host_time = t;
94 info->yield_start_cycle = t;
96 info->time_state.last_update = 0;
97 info->time_state.guest_cycles = 0;
98 PrintDebug("Starting time for core %d at host time %llu/guest time %llu.\n",
99 info->vcpu_id, t, info->time_state.guest_cycles);
105 host_to_guest_cycles(struct guest_info * info, sint64_t host_cycles) {
106 struct vm_core_time * core_time_state = &(info->time_state);
107 uint32_t cl_num, cl_denom;
109 cl_num = core_time_state->clock_ratio_num;
110 cl_denom = core_time_state->clock_ratio_denom;
112 return (host_cycles * cl_num) / cl_denom;
117 guest_to_host_cycles(struct guest_info * info, sint64_t guest_cycles) {
118 struct vm_core_time * core_time_state = &(info->time_state);
119 uint32_t cl_num, cl_denom;
121 cl_num = core_time_state->clock_ratio_num;
122 cl_denom = core_time_state->clock_ratio_denom;
124 return (guest_cycles * cl_denom) / cl_num;
128 int v3_advance_time(struct guest_info * info, uint64_t *host_cycles)
130 uint64_t guest_cycles;
132 if (info->time_state.flags & VM_TIME_SLAVE_HOST) {
133 struct v3_time *vm_ts = &(info->vm_info->time_state);
134 uint64_t ht = v3_get_host_time(&info->time_state);
135 uint64_t host_elapsed = ht - info->time_state.initial_host_time;
136 uint64_t dilated_elapsed = (host_elapsed * vm_ts->td_num) / vm_ts->td_denom;
137 uint64_t guest_elapsed = host_to_guest_cycles(info, dilated_elapsed);
138 guest_cycles = guest_elapsed - v3_get_guest_time(&info->time_state);
139 } else if (host_cycles) {
140 guest_cycles = host_to_guest_cycles(info, *host_cycles);
145 info->time_state.guest_cycles += guest_cycles;
150 struct v3_timer * v3_add_timer(struct guest_info * info,
151 struct v3_timer_ops * ops,
152 void * private_data) {
153 struct v3_timer * timer = NULL;
154 timer = (struct v3_timer *)V3_Malloc(sizeof(struct v3_timer));
155 V3_ASSERT(timer != NULL);
158 timer->private_data = private_data;
160 list_add(&(timer->timer_link), &(info->time_state.timers));
161 info->time_state.num_timers++;
166 int v3_remove_timer(struct guest_info * info, struct v3_timer * timer) {
167 list_del(&(timer->timer_link));
168 info->time_state.num_timers--;
174 void v3_update_timers(struct guest_info * info) {
175 struct vm_core_time *time_state = &info->time_state;
176 struct v3_timer * tmp_timer;
178 uint64_t old_time = time_state->last_update;
180 time_state->last_update = v3_get_guest_time(time_state);
181 cycles = (sint64_t)(time_state->last_update - old_time);
183 PrintError("Cycles appears to have rolled over - old time %lld, current time %lld.\n",
184 old_time, time_state->last_update);
188 //PrintDebug("Updating timers with %lld elapsed cycles.\n", cycles);
189 list_for_each_entry(tmp_timer, &(time_state->timers), timer_link) {
190 tmp_timer->ops->update_timer(info, cycles, time_state->guest_cpu_freq, tmp_timer->private_data);
196 * Handle full virtualization of the time stamp counter. As noted
197 * above, we don't store the actual value of the TSC, only the guest's
198 * offset from monotonic guest's time. If the guest writes to the TSC, we
199 * handle this by changing that offset.
201 * Possible TODO: Proper hooking of TSC read/writes?
204 int v3_rdtsc(struct guest_info * info) {
205 uint64_t tscval = v3_get_guest_tsc(&info->time_state);
207 info->vm_regs.rdx = tscval >> 32;
208 info->vm_regs.rax = tscval & 0xffffffffLL;
213 int v3_handle_rdtsc(struct guest_info * info) {
214 PrintDebug("Handling virtual RDTSC call.\n");
217 info->vm_regs.rax &= 0x00000000ffffffffLL;
218 info->vm_regs.rdx &= 0x00000000ffffffffLL;
225 int v3_rdtscp(struct guest_info * info) {
227 /* First get the MSR value that we need. It's safe to futz with
228 * ra/c/dx here since they're modified by this instruction anyway. */
229 info->vm_regs.rcx = TSC_AUX_MSR;
230 ret = v3_handle_msr_read(info);
236 info->vm_regs.rcx = info->vm_regs.rax;
238 /* Now do the TSC half of the instruction */
239 ret = v3_rdtsc(info);
249 int v3_handle_rdtscp(struct guest_info * info) {
250 PrintDebug("Handling virtual RDTSCP call.\n");
254 info->vm_regs.rax &= 0x00000000ffffffffLL;
255 info->vm_regs.rcx &= 0x00000000ffffffffLL;
256 info->vm_regs.rdx &= 0x00000000ffffffffLL;
263 static int tsc_aux_msr_read_hook(struct guest_info *info, uint_t msr_num,
264 struct v3_msr *msr_val, void *priv) {
265 struct vm_core_time * time_state = &(info->time_state);
267 V3_ASSERT(msr_num == TSC_AUX_MSR);
269 msr_val->lo = time_state->tsc_aux.lo;
270 msr_val->hi = time_state->tsc_aux.hi;
275 static int tsc_aux_msr_write_hook(struct guest_info *info, uint_t msr_num,
276 struct v3_msr msr_val, void *priv) {
277 struct vm_core_time * time_state = &(info->time_state);
279 V3_ASSERT(msr_num == TSC_AUX_MSR);
281 time_state->tsc_aux.lo = msr_val.lo;
282 time_state->tsc_aux.hi = msr_val.hi;
287 static int tsc_msr_read_hook(struct guest_info *info, uint_t msr_num,
288 struct v3_msr *msr_val, void *priv) {
289 uint64_t time = v3_get_guest_tsc(&info->time_state);
291 PrintDebug("Handling virtual TSC MSR read call.\n");
292 V3_ASSERT(msr_num == TSC_MSR);
294 msr_val->hi = time >> 32;
295 msr_val->lo = time & 0xffffffffLL;
300 static int tsc_msr_write_hook(struct guest_info *info, uint_t msr_num,
301 struct v3_msr msr_val, void *priv) {
302 struct vm_core_time * time_state = &(info->time_state);
303 uint64_t guest_time, new_tsc;
305 PrintDebug("Handling virtual TSC MSR write call.\n");
306 V3_ASSERT(msr_num == TSC_MSR);
308 new_tsc = (((uint64_t)msr_val.hi) << 32) | (uint64_t)msr_val.lo;
309 guest_time = v3_get_guest_time(time_state);
310 time_state->tsc_guest_offset = (sint64_t)(new_tsc - guest_time);
316 handle_time_configuration(struct v3_vm_info * vm, v3_cfg_tree_t *cfg) {
317 char *source, *dilation;
319 vm->time_state.flags = V3_TIME_SLAVE_HOST;
320 vm->time_state.td_num = vm->time_state.td_denom = 1;
324 source = v3_cfg_val(cfg, "source");
326 if (strcasecmp(source, "none") == 0) {
327 vm->time_state.flags &= ~V3_TIME_SLAVE_HOST;
328 } else if (strcasecmp(source, "host") != 0) {
329 PrintError("Unknown time source for VM core time management.\n");
331 PrintDebug("VM time slaved to host TSC.\n");
335 dilation = v3_cfg_val(cfg, "dilation");
337 if (!(vm->time_state.flags & VM_TIME_SLAVE_HOST)) {
338 PrintError("Time dilation only valid when slaved to host time.\n");
340 uint32_t num = 1, denom = 1;
341 denom = atoi(dilation);
342 if ((num > 0) && (denom > 0)) {
343 vm->time_state.td_num = num;
344 vm->time_state.td_denom = denom;
347 if ((vm->time_state.td_num != 1)
348 || (vm->time_state.td_denom != 1)) {
349 V3_Print("Time dilated from host time by a factor of %d/%d"
350 " in guest.\n", vm->time_state.td_denom,
351 vm->time_state.td_num);
353 PrintError("Time dilation specifier in configuration did not"
354 " result in actual time dilation in VM.\n");
360 int v3_init_time_vm(struct v3_vm_info * vm) {
361 v3_cfg_tree_t * cfg_tree = vm->cfg_data->cfg;
364 PrintDebug("Installing TSC MSR hook.\n");
365 ret = v3_hook_msr(vm, TSC_MSR,
366 tsc_msr_read_hook, tsc_msr_write_hook, NULL);
372 PrintDebug("Installing TSC_AUX MSR hook.\n");
373 ret = v3_hook_msr(vm, TSC_AUX_MSR, tsc_aux_msr_read_hook,
374 tsc_aux_msr_write_hook, NULL);
380 PrintDebug("Registering TIME_CPUFREQ hypercall.\n");
381 ret = v3_register_hypercall(vm, TIME_CPUFREQ_HCALL,
382 handle_cpufreq_hcall, NULL);
384 handle_time_configuration(vm, v3_cfg_subtree(cfg_tree, "time"));
389 void v3_deinit_time_vm(struct v3_vm_info * vm) {
390 v3_unhook_msr(vm, TSC_MSR);
391 v3_unhook_msr(vm, TSC_AUX_MSR);
393 v3_remove_hypercall(vm, TIME_CPUFREQ_HCALL);
397 gcd ( uint32_t a, uint32_t b )
401 c = a; a = b%a; b = c;
406 static int compute_core_ratios(struct guest_info * info,
407 uint32_t hostKhz, uint32_t guestKhz)
409 struct vm_core_time * time_state = &(info->time_state);
412 /* Compute these using the GCD() of the guest and host CPU freq.
413 * If the GCD is too small, make it "big enough" */
414 khzGCD = gcd(hostKhz, guestKhz);
418 time_state->clock_ratio_num = guestKhz / khzGCD;
419 time_state->clock_ratio_denom = hostKhz / khzGCD;
421 time_state->ipc_ratio_num = 1;
422 time_state->ipc_ratio_denom = 1;
427 void v3_init_time_core(struct guest_info * info) {
428 struct vm_core_time * time_state = &(info->time_state);
429 v3_cfg_tree_t * cfg_tree = info->core_cfg_data;
432 time_state->host_cpu_freq = V3_CPU_KHZ();
433 khz = v3_cfg_val(cfg_tree, "khz");
436 time_state->guest_cpu_freq = atoi(khz);
437 PrintDebug("Logical Core %d (vcpu=%d) CPU frequency requested at %d khz.\n",
438 info->pcpu_id, info->vcpu_id, time_state->guest_cpu_freq);
441 if ( (khz == NULL) ||
442 (time_state->guest_cpu_freq <= 0)) {
443 /* || (time_state->guest_cpu_freq > time_state->host_cpu_freq) ) { */
444 time_state->guest_cpu_freq = time_state->host_cpu_freq;
446 compute_core_ratios(info, time_state->host_cpu_freq,
447 time_state->guest_cpu_freq);
449 time_state->flags = 0;
450 if (info->vm_info->time_state.flags & V3_TIME_SLAVE_HOST) {
451 time_state->flags |= VM_TIME_SLAVE_HOST;
453 if ((time_state->clock_ratio_denom != 1) ||
454 (time_state->clock_ratio_num != 1)) {
455 time_state->flags |= VM_TIME_TRAP_RDTSC;
458 PrintDebug("Logical Core %d (vcpu=%d) CPU frequency set to %d KHz (host CPU frequency = %d KHz).\n",
459 info->pcpu_id, info->vcpu_id,
460 time_state->guest_cpu_freq,
461 time_state->host_cpu_freq);
462 PrintDebug(" td_mult = %d/%d, cl_mult = %u/%u, ipc_mult = %u/%u.\n",
463 info->vm_info->time_state.td_num,
464 info->vm_info->time_state.td_denom,
465 time_state->clock_ratio_num, time_state->clock_ratio_denom,
466 time_state->ipc_ratio_num, time_state->ipc_ratio_denom);
467 PrintDebug(" source = %s, rdtsc trapping = %s\n",
468 (time_state->flags & VM_TIME_SLAVE_HOST) ? "host" : "none",
469 (time_state->flags & VM_TIME_TRAP_RDTSC) ? "true" : "false");
471 time_state->guest_cycles = 0;
472 time_state->tsc_guest_offset = 0;
473 time_state->last_update = 0;
474 time_state->initial_host_time = 0;
476 INIT_LIST_HEAD(&(time_state->timers));
477 time_state->num_timers = 0;
479 time_state->tsc_aux.lo = 0;
480 time_state->tsc_aux.hi = 0;
484 void v3_deinit_time_core(struct guest_info * core) {
485 struct vm_core_time * time_state = &(core->time_state);
486 struct v3_timer * tmr = NULL;
487 struct v3_timer * tmp = NULL;
489 list_for_each_entry_safe(tmr, tmp, &(time_state->timers), timer_link) {
490 v3_remove_timer(core, tmr);