X-Git-Url: http://v3vee.org/palacios/gitweb/gitweb.cgi?a=blobdiff_plain;f=palacios%2Fsrc%2Fpalacios%2Fvmm_time.c;h=44affe42f5513b2560ca3ae73cda813c7c528fed;hb=07a12ade201ee7c2fe2358084ca079d2facac500;hp=7814acb215a38ac3b9c26ec26ab8f40aa01d400f;hpb=ccd9ddb5d9279fe8fcdacfc3bcd466eb3da70791;p=palacios.git diff --git a/palacios/src/palacios/vmm_time.c b/palacios/src/palacios/vmm_time.c index 7814acb..44affe4 100644 --- a/palacios/src/palacios/vmm_time.c +++ b/palacios/src/palacios/vmm_time.c @@ -27,10 +27,52 @@ #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 using an offsets 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. + * + * The value used to offset the guest TSC from the host TSC is the *sum* of all + * of these offsets (2 and 3) above + * + * 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). + * + * Future additions: + * (1) Add support for temporarily skewing guest time off of where it should + * be to support slack simulation of guests. The idea is that simulators + * set this skew to be the difference between how much time passed for a + * simulated feature and a real implementation of that feature, making + * pass at a different rate from real time on this core. The VMM will then + * attempt to move this skew back towards 0 subject to resolution/accuracy + * constraints from various system timers. + * + * The main effort in doing this will be to get accuracy/resolution + * information from each local timer and to use this to bound how much skew + * is removed on each exit. + */ + + 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); @@ -39,53 +81,44 @@ static int handle_cpufreq_hcall(struct guest_info * info, uint_t hcall_id, void -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; -} +// 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); -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 (time_state->host_cpu_freq == time_state->guest_cpu_freq) { + time_state->guest_host_offset = 0; + } else { + uint64_t guest_time, guest_elapsed, desired_elapsed; + uint64_t host_time, target_host_time; + guest_time = v3_get_guest_time(time_state); + + /* Compute what host time this guest time should correspond to. */ + guest_elapsed = (guest_time - time_state->initial_time); + desired_elapsed = (guest_elapsed * time_state->host_cpu_freq) / time_state->guest_cpu_freq; + target_host_time = time_state->initial_time + desired_elapsed; + + /* Yield until that host time is reached */ + host_time = v3_get_host_time(time_state); + while (host_time < target_host_time) { + v3_yield(info); + host_time = v3_get_host_time(time_state); + } + + time_state->guest_host_offset = (sint64_t)guest_time - (sint64_t)host_time; + } return 0; } @@ -104,7 +137,6 @@ int v3_add_timer(struct guest_info * info, struct vm_timer_ops * ops, return 0; } - int v3_remove_timer(struct guest_info * info, struct vm_timer * timer) { list_del(&(timer->timer_link)); info->time_state.num_timers--; @@ -122,6 +154,173 @@ void v3_update_timers(struct guest_info * info) { 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 monotonic guest's time. If the guest writes to the TSC, we + * handle this by changing that offset. + * + * Possible TODO: Proper hooking of TSC read/writes? + */ + +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 */ + 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); + v3_cfg_tree_t * cfg_tree = info->core_cfg_data; + static int one_time = 0; + char *khz; + + time_state->host_cpu_freq = V3_CPU_KHZ(); + khz = v3_cfg_val(cfg_tree, "khz"); + if (khz) { + time_state->guest_cpu_freq = atoi(khz); + PrintDebug("Core %d CPU frequency requested at %d khz.\n", + info->cpu_id, time_state->guest_cpu_freq); + } + + if (!khz || time_state->guest_cpu_freq > time_state->host_cpu_freq) { + time_state->guest_cpu_freq = time_state->host_cpu_freq; + } + PrintDebug("Core %d CPU frequency set to %d KHz (host CPU frequency = %d KHz).\n", info->cpu_id, time_state->guest_cpu_freq, time_state->host_cpu_freq); + + 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; + } +} + + + + + + + + +