linux/arch/x86/kernel/kvmclock.c
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   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/kvmclock.h>
  24
  25static int kvmclock __initdata = 1;
  26static int kvmclock_vsyscall __initdata = 1;
  27static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
  28static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
  29static u64 kvm_sched_clock_offset __ro_after_init;
  30
  31static int __init parse_no_kvmclock(char *arg)
  32{
  33        kvmclock = 0;
  34        return 0;
  35}
  36early_param("no-kvmclock", parse_no_kvmclock);
  37
  38static int __init parse_no_kvmclock_vsyscall(char *arg)
  39{
  40        kvmclock_vsyscall = 0;
  41        return 0;
  42}
  43early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
  44
  45/* Aligned to page sizes to match whats mapped via vsyscalls to userspace */
  46#define HVC_BOOT_ARRAY_SIZE \
  47        (PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info))
  48
  49static struct pvclock_vsyscall_time_info
  50                        hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
  51static struct pvclock_wall_clock wall_clock __bss_decrypted;
  52static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
  53static struct pvclock_vsyscall_time_info *hvclock_mem;
  54
  55static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
  56{
  57        return &this_cpu_read(hv_clock_per_cpu)->pvti;
  58}
  59
  60static inline struct pvclock_vsyscall_time_info *this_cpu_hvclock(void)
  61{
  62        return this_cpu_read(hv_clock_per_cpu);
  63}
  64
  65/*
  66 * The wallclock is the time of day when we booted. Since then, some time may
  67 * have elapsed since the hypervisor wrote the data. So we try to account for
  68 * that with system time
  69 */
  70static void kvm_get_wallclock(struct timespec64 *now)
  71{
  72        wrmsrl(msr_kvm_wall_clock, slow_virt_to_phys(&wall_clock));
  73        preempt_disable();
  74        pvclock_read_wallclock(&wall_clock, this_cpu_pvti(), now);
  75        preempt_enable();
  76}
  77
  78static int kvm_set_wallclock(const struct timespec64 *now)
  79{
  80        return -ENODEV;
  81}
  82
  83static u64 kvm_clock_read(void)
  84{
  85        u64 ret;
  86
  87        preempt_disable_notrace();
  88        ret = pvclock_clocksource_read(this_cpu_pvti());
  89        preempt_enable_notrace();
  90        return ret;
  91}
  92
  93static u64 kvm_clock_get_cycles(struct clocksource *cs)
  94{
  95        return kvm_clock_read();
  96}
  97
  98static u64 kvm_sched_clock_read(void)
  99{
 100        return kvm_clock_read() - kvm_sched_clock_offset;
 101}
 102
 103static inline void kvm_sched_clock_init(bool stable)
 104{
 105        if (!stable)
 106                clear_sched_clock_stable();
 107        kvm_sched_clock_offset = kvm_clock_read();
 108        paravirt_set_sched_clock(kvm_sched_clock_read);
 109
 110        pr_info("kvm-clock: using sched offset of %llu cycles",
 111                kvm_sched_clock_offset);
 112
 113        BUILD_BUG_ON(sizeof(kvm_sched_clock_offset) >
 114                sizeof(((struct pvclock_vcpu_time_info *)NULL)->system_time));
 115}
 116
 117/*
 118 * If we don't do that, there is the possibility that the guest
 119 * will calibrate under heavy load - thus, getting a lower lpj -
 120 * and execute the delays themselves without load. This is wrong,
 121 * because no delay loop can finish beforehand.
 122 * Any heuristics is subject to fail, because ultimately, a large
 123 * poll of guests can be running and trouble each other. So we preset
 124 * lpj here
 125 */
 126static unsigned long kvm_get_tsc_khz(void)
 127{
 128        setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 129        return pvclock_tsc_khz(this_cpu_pvti());
 130}
 131
 132static void __init kvm_get_preset_lpj(void)
 133{
 134        unsigned long khz;
 135        u64 lpj;
 136
 137        khz = kvm_get_tsc_khz();
 138
 139        lpj = ((u64)khz * 1000);
 140        do_div(lpj, HZ);
 141        preset_lpj = lpj;
 142}
 143
 144bool kvm_check_and_clear_guest_paused(void)
 145{
 146        struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
 147        bool ret = false;
 148
 149        if (!src)
 150                return ret;
 151
 152        if ((src->pvti.flags & PVCLOCK_GUEST_STOPPED) != 0) {
 153                src->pvti.flags &= ~PVCLOCK_GUEST_STOPPED;
 154                pvclock_touch_watchdogs();
 155                ret = true;
 156        }
 157        return ret;
 158}
 159
 160static int kvm_cs_enable(struct clocksource *cs)
 161{
 162        vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
 163        return 0;
 164}
 165
 166struct clocksource kvm_clock = {
 167        .name   = "kvm-clock",
 168        .read   = kvm_clock_get_cycles,
 169        .rating = 400,
 170        .mask   = CLOCKSOURCE_MASK(64),
 171        .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
 172        .enable = kvm_cs_enable,
 173};
 174EXPORT_SYMBOL_GPL(kvm_clock);
 175
 176static void kvm_register_clock(char *txt)
 177{
 178        struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
 179        u64 pa;
 180
 181        if (!src)
 182                return;
 183
 184        pa = slow_virt_to_phys(&src->pvti) | 0x01ULL;
 185        wrmsrl(msr_kvm_system_time, pa);
 186        pr_info("kvm-clock: cpu %d, msr %llx, %s", smp_processor_id(), pa, txt);
 187}
 188
 189static void kvm_save_sched_clock_state(void)
 190{
 191}
 192
 193static void kvm_restore_sched_clock_state(void)
 194{
 195        kvm_register_clock("primary cpu clock, resume");
 196}
 197
 198#ifdef CONFIG_X86_LOCAL_APIC
 199static void kvm_setup_secondary_clock(void)
 200{
 201        kvm_register_clock("secondary cpu clock");
 202}
 203#endif
 204
 205void kvmclock_disable(void)
 206{
 207        native_write_msr(msr_kvm_system_time, 0, 0);
 208}
 209
 210static void __init kvmclock_init_mem(void)
 211{
 212        unsigned long ncpus;
 213        unsigned int order;
 214        struct page *p;
 215        int r;
 216
 217        if (HVC_BOOT_ARRAY_SIZE >= num_possible_cpus())
 218                return;
 219
 220        ncpus = num_possible_cpus() - HVC_BOOT_ARRAY_SIZE;
 221        order = get_order(ncpus * sizeof(*hvclock_mem));
 222
 223        p = alloc_pages(GFP_KERNEL, order);
 224        if (!p) {
 225                pr_warn("%s: failed to alloc %d pages", __func__, (1U << order));
 226                return;
 227        }
 228
 229        hvclock_mem = page_address(p);
 230
 231        /*
 232         * hvclock is shared between the guest and the hypervisor, must
 233         * be mapped decrypted.
 234         */
 235        if (sev_active()) {
 236                r = set_memory_decrypted((unsigned long) hvclock_mem,
 237                                         1UL << order);
 238                if (r) {
 239                        __free_pages(p, order);
 240                        hvclock_mem = NULL;
 241                        pr_warn("kvmclock: set_memory_decrypted() failed. Disabling\n");
 242                        return;
 243                }
 244        }
 245
 246        memset(hvclock_mem, 0, PAGE_SIZE << order);
 247}
 248
 249static int __init kvm_setup_vsyscall_timeinfo(void)
 250{
 251        kvmclock_init_mem();
 252
 253#ifdef CONFIG_X86_64
 254        if (per_cpu(hv_clock_per_cpu, 0) && kvmclock_vsyscall) {
 255                u8 flags;
 256
 257                flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
 258                if (!(flags & PVCLOCK_TSC_STABLE_BIT))
 259                        return 0;
 260
 261                kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
 262        }
 263#endif
 264
 265        return 0;
 266}
 267early_initcall(kvm_setup_vsyscall_timeinfo);
 268
 269static int kvmclock_setup_percpu(unsigned int cpu)
 270{
 271        struct pvclock_vsyscall_time_info *p = per_cpu(hv_clock_per_cpu, cpu);
 272
 273        /*
 274         * The per cpu area setup replicates CPU0 data to all cpu
 275         * pointers. So carefully check. CPU0 has been set up in init
 276         * already.
 277         */
 278        if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
 279                return 0;
 280
 281        /* Use the static page for the first CPUs, allocate otherwise */
 282        if (cpu < HVC_BOOT_ARRAY_SIZE)
 283                p = &hv_clock_boot[cpu];
 284        else if (hvclock_mem)
 285                p = hvclock_mem + cpu - HVC_BOOT_ARRAY_SIZE;
 286        else
 287                return -ENOMEM;
 288
 289        per_cpu(hv_clock_per_cpu, cpu) = p;
 290        return p ? 0 : -ENOMEM;
 291}
 292
 293void __init kvmclock_init(void)
 294{
 295        u8 flags;
 296
 297        if (!kvm_para_available() || !kvmclock)
 298                return;
 299
 300        if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
 301                msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
 302                msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
 303        } else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
 304                return;
 305        }
 306
 307        if (cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu",
 308                              kvmclock_setup_percpu, NULL) < 0) {
 309                return;
 310        }
 311
 312        pr_info("kvm-clock: Using msrs %x and %x",
 313                msr_kvm_system_time, msr_kvm_wall_clock);
 314
 315        this_cpu_write(hv_clock_per_cpu, &hv_clock_boot[0]);
 316        kvm_register_clock("primary cpu clock");
 317        pvclock_set_pvti_cpu0_va(hv_clock_boot);
 318
 319        if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
 320                pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
 321
 322        flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
 323        kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
 324
 325        x86_platform.calibrate_tsc = kvm_get_tsc_khz;
 326        x86_platform.calibrate_cpu = kvm_get_tsc_khz;
 327        x86_platform.get_wallclock = kvm_get_wallclock;
 328        x86_platform.set_wallclock = kvm_set_wallclock;
 329#ifdef CONFIG_X86_LOCAL_APIC
 330        x86_cpuinit.early_percpu_clock_init = kvm_setup_secondary_clock;
 331#endif
 332        x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
 333        x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
 334        kvm_get_preset_lpj();
 335
 336        /*
 337         * X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
 338         * with P/T states and does not stop in deep C-states.
 339         *
 340         * Invariant TSC exposed by host means kvmclock is not necessary:
 341         * can use TSC as clocksource.
 342         *
 343         */
 344        if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
 345            boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
 346            !check_tsc_unstable())
 347                kvm_clock.rating = 299;
 348
 349        clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
 350        pv_info.name = "KVM";
 351}
 352
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