arch/x86/kernel/kvmclock.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*  KVM paravirtual clock driver. A clocksource implementation
   3     Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.
   4 */
   5
   6 #include <linux/clocksource.h>
   7 #include <linux/kvm_para.h>
   8 #include <asm/pvclock.h>
   9 #include <asm/msr.h>
  10 #include <asm/apic.h>
  11 #include <linux/percpu.h>
  12 #include <linux/hardirq.h>
  13 #include <linux/cpuhotplug.h>
  14 #include <linux/sched.h>
  15 #include <linux/sched/clock.h>
  16 #include <linux/mm.h>
  17 #include <linux/slab.h>
  18 #include <linux/set_memory.h>
  19
  20 #include <asm/hypervisor.h>
  21 #include <asm/mem_encrypt.h>
  22 #include <asm/x86_init.h>
  23 #include <asm/reboot.h>
  24 #include <asm/kvmclock.h>
  25
  26 static int kvmclock __initdata = 1;
  27 static int kvmclock_vsyscall __initdata = 1;
  28 static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
  29 static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
  30 static u64 kvm_sched_clock_offset __ro_after_init;
  31
  32 static int __init parse_no_kvmclock(char *arg)
  33 {
  34         kvmclock = 0;
  35         return 0;
  36 }
  37 early_param("no-kvmclock", parse_no_kvmclock);
  38
  39 static int __init parse_no_kvmclock_vsyscall(char *arg)
  40 {
  41         kvmclock_vsyscall = 0;
  42         return 0;
  43 }
  44 early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
  45
  46 /* Aligned to page sizes to match whats mapped via vsyscalls to userspace */
  47 #define HV_CLOCK_SIZE   (sizeof(struct pvclock_vsyscall_time_info) * NR_CPUS)
  48 #define HVC_BOOT_ARRAY_SIZE \
  49         (PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info))
  50
  51 static struct pvclock_vsyscall_time_info
  52                         hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
  53 static struct pvclock_wall_clock wall_clock __bss_decrypted;
  54 static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
  55 static struct pvclock_vsyscall_time_info *hvclock_mem;
  56
  57 static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
  58 {
  59         return &this_cpu_read(hv_clock_per_cpu)->pvti;
  60 }
  61
  62 static inline struct pvclock_vsyscall_time_info *this_cpu_hvclock(void)
  63 {
  64         return this_cpu_read(hv_clock_per_cpu);
  65 }
  66
  67 /*
  68  * The wallclock is the time of day when we booted. Since then, some time may
  69  * have elapsed since the hypervisor wrote the data. So we try to account for
  70  * that with system time
  71  */
  72 static void kvm_get_wallclock(struct timespec64 *now)
  73 {
  74         wrmsrl(msr_kvm_wall_clock, slow_virt_to_phys(&wall_clock));
  75         preempt_disable();
  76         pvclock_read_wallclock(&wall_clock, this_cpu_pvti(), now);
  77         preempt_enable();
  78 }
  79
  80 static int kvm_set_wallclock(const struct timespec64 *now)
  81 {
  82         return -ENODEV;
  83 }
  84
  85 static u64 kvm_clock_read(void)
  86 {
  87         u64 ret;
  88
  89         preempt_disable_notrace();
  90         ret = pvclock_clocksource_read(this_cpu_pvti());
  91         preempt_enable_notrace();
  92         return ret;
  93 }
  94
  95 static u64 kvm_clock_get_cycles(struct clocksource *cs)
  96 {
  97         return kvm_clock_read();
  98 }
  99
 100 static u64 kvm_sched_clock_read(void)
 101 {
 102         return kvm_clock_read() - kvm_sched_clock_offset;
 103 }
 104
 105 static inline void kvm_sched_clock_init(bool stable)
 106 {
 107         if (!stable)
 108                 clear_sched_clock_stable();
 109         kvm_sched_clock_offset = kvm_clock_read();
 110         pv_ops.time.sched_clock = kvm_sched_clock_read;
 111
 112         pr_info("kvm-clock: using sched offset of %llu cycles",
 113                 kvm_sched_clock_offset);
 114
 115         BUILD_BUG_ON(sizeof(kvm_sched_clock_offset) >
 116                 sizeof(((struct pvclock_vcpu_time_info *)NULL)->system_time));
 117 }
 118
 119 /*
 120  * If we don't do that, there is the possibility that the guest
 121  * will calibrate under heavy load - thus, getting a lower lpj -
 122  * and execute the delays themselves without load. This is wrong,
 123  * because no delay loop can finish beforehand.
 124  * Any heuristics is subject to fail, because ultimately, a large
 125  * poll of guests can be running and trouble each other. So we preset
 126  * lpj here
 127  */
 128 static unsigned long kvm_get_tsc_khz(void)
 129 {
 130         setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 131         return pvclock_tsc_khz(this_cpu_pvti());
 132 }
 133
 134 static void __init kvm_get_preset_lpj(void)
 135 {
 136         unsigned long khz;
 137         u64 lpj;
 138
 139         khz = kvm_get_tsc_khz();
 140
 141         lpj = ((u64)khz * 1000);
 142         do_div(lpj, HZ);
 143         preset_lpj = lpj;
 144 }
 145
 146 bool kvm_check_and_clear_guest_paused(void)
 147 {
 148         struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
 149         bool ret = false;
 150
 151         if (!src)
 152                 return ret;
 153
 154         if ((src->pvti.flags & PVCLOCK_GUEST_STOPPED) != 0) {
 155                 src->pvti.flags &= ~PVCLOCK_GUEST_STOPPED;
 156                 pvclock_touch_watchdogs();
 157                 ret = true;
 158         }
 159         return ret;
 160 }
 161
 162 static int kvm_cs_enable(struct clocksource *cs)
 163 {
 164         vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
 165         return 0;
 166 }
 167
 168 struct clocksource kvm_clock = {
 169         .name   = "kvm-clock",
 170         .read   = kvm_clock_get_cycles,
 171         .rating = 400,
 172         .mask   = CLOCKSOURCE_MASK(64),
 173         .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
 174         .enable = kvm_cs_enable,
 175 };
 176 EXPORT_SYMBOL_GPL(kvm_clock);
 177
 178 static void kvm_register_clock(char *txt)
 179 {
 180         struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
 181         u64 pa;
 182
 183         if (!src)
 184                 return;
 185
 186         pa = slow_virt_to_phys(&src->pvti) | 0x01ULL;
 187         wrmsrl(msr_kvm_system_time, pa);
 188         pr_info("kvm-clock: cpu %d, msr %llx, %s", smp_processor_id(), pa, txt);
 189 }
 190
 191 static void kvm_save_sched_clock_state(void)
 192 {
 193 }
 194
 195 static void kvm_restore_sched_clock_state(void)
 196 {
 197         kvm_register_clock("primary cpu clock, resume");
 198 }
 199
 200 #ifdef CONFIG_X86_LOCAL_APIC
 201 static void kvm_setup_secondary_clock(void)
 202 {
 203         kvm_register_clock("secondary cpu clock");
 204 }
 205 #endif
 206
 207 /*
 208  * After the clock is registered, the host will keep writing to the
 209  * registered memory location. If the guest happens to shutdown, this memory
 210  * won't be valid. In cases like kexec, in which you install a new kernel, this
 211  * means a random memory location will be kept being written. So before any
 212  * kind of shutdown from our side, we unregister the clock by writing anything
 213  * that does not have the 'enable' bit set in the msr
 214  */
 215 #ifdef CONFIG_KEXEC_CORE
 216 static void kvm_crash_shutdown(struct pt_regs *regs)
 217 {
 218         native_write_msr(msr_kvm_system_time, 0, 0);
 219         kvm_disable_steal_time();
 220         native_machine_crash_shutdown(regs);
 221 }
 222 #endif
 223
 224 static void kvm_shutdown(void)
 225 {
 226         native_write_msr(msr_kvm_system_time, 0, 0);
 227         kvm_disable_steal_time();
 228         native_machine_shutdown();
 229 }
 230
 231 static void __init kvmclock_init_mem(void)
 232 {
 233         unsigned long ncpus;
 234         unsigned int order;
 235         struct page *p;
 236         int r;
 237
 238         if (HVC_BOOT_ARRAY_SIZE >= num_possible_cpus())
 239                 return;
 240
 241         ncpus = num_possible_cpus() - HVC_BOOT_ARRAY_SIZE;
 242         order = get_order(ncpus * sizeof(*hvclock_mem));
 243
 244         p = alloc_pages(GFP_KERNEL, order);
 245         if (!p) {
 246                 pr_warn("%s: failed to alloc %d pages", __func__, (1U << order));
 247                 return;
 248         }
 249
 250         hvclock_mem = page_address(p);
 251
 252         /*
 253          * hvclock is shared between the guest and the hypervisor, must
 254          * be mapped decrypted.
 255          */
 256         if (sev_active()) {
 257                 r = set_memory_decrypted((unsigned long) hvclock_mem,
 258                                          1UL << order);
 259                 if (r) {
 260                         __free_pages(p, order);
 261                         hvclock_mem = NULL;
 262                         pr_warn("kvmclock: set_memory_decrypted() failed. Disabling\n");
 263                         return;
 264                 }
 265         }
 266
 267         memset(hvclock_mem, 0, PAGE_SIZE << order);
 268 }
 269
 270 static int __init kvm_setup_vsyscall_timeinfo(void)
 271 {
 272 #ifdef CONFIG_X86_64
 273         u8 flags;
 274
 275         if (!per_cpu(hv_clock_per_cpu, 0) || !kvmclock_vsyscall)
 276                 return 0;
 277
 278         flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
 279         if (!(flags & PVCLOCK_TSC_STABLE_BIT))
 280                 return 0;
 281
 282         kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
 283 #endif
 284
 285         kvmclock_init_mem();
 286
 287         return 0;
 288 }
 289 early_initcall(kvm_setup_vsyscall_timeinfo);
 290
 291 static int kvmclock_setup_percpu(unsigned int cpu)
 292 {
 293         struct pvclock_vsyscall_time_info *p = per_cpu(hv_clock_per_cpu, cpu);
 294
 295         /*
 296          * The per cpu area setup replicates CPU0 data to all cpu
 297          * pointers. So carefully check. CPU0 has been set up in init
 298          * already.
 299          */
 300         if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
 301                 return 0;
 302
 303         /* Use the static page for the first CPUs, allocate otherwise */
 304         if (cpu < HVC_BOOT_ARRAY_SIZE)
 305                 p = &hv_clock_boot[cpu];
 306         else if (hvclock_mem)
 307                 p = hvclock_mem + cpu - HVC_BOOT_ARRAY_SIZE;
 308         else
 309                 return -ENOMEM;
 310
 311         per_cpu(hv_clock_per_cpu, cpu) = p;
 312         return p ? 0 : -ENOMEM;
 313 }
 314
 315 void __init kvmclock_init(void)
 316 {
 317         u8 flags;
 318
 319         if (!kvm_para_available() || !kvmclock)
 320                 return;
 321
 322         if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
 323                 msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
 324                 msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
 325         } else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
 326                 return;
 327         }
 328
 329         if (cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu",
 330                               kvmclock_setup_percpu, NULL) < 0) {
 331                 return;
 332         }
 333
 334         pr_info("kvm-clock: Using msrs %x and %x",
 335                 msr_kvm_system_time, msr_kvm_wall_clock);
 336
 337         this_cpu_write(hv_clock_per_cpu, &hv_clock_boot[0]);
 338         kvm_register_clock("primary cpu clock");
 339         pvclock_set_pvti_cpu0_va(hv_clock_boot);
 340
 341         if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
 342                 pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
 343
 344         flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
 345         kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
 346
 347         x86_platform.calibrate_tsc = kvm_get_tsc_khz;
 348         x86_platform.calibrate_cpu = kvm_get_tsc_khz;
 349         x86_platform.get_wallclock = kvm_get_wallclock;
 350         x86_platform.set_wallclock = kvm_set_wallclock;
 351 #ifdef CONFIG_X86_LOCAL_APIC
 352         x86_cpuinit.early_percpu_clock_init = kvm_setup_secondary_clock;
 353 #endif
 354         x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
 355         x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
 356         machine_ops.shutdown  = kvm_shutdown;
 357 #ifdef CONFIG_KEXEC_CORE
 358         machine_ops.crash_shutdown  = kvm_crash_shutdown;
 359 #endif
 360         kvm_get_preset_lpj();
 361
 362         /*
 363          * X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
 364          * with P/T states and does not stop in deep C-states.
 365          *
 366          * Invariant TSC exposed by host means kvmclock is not necessary:
 367          * can use TSC as clocksource.
 368          *
 369          */
 370         if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
 371             boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
 372             !check_tsc_unstable())
 373                 kvm_clock.rating = 299;
 374
 375         clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
 376         pv_info.name = "KVM";
 377 }