// SPDX-License-Identifier: GPL-2.0-or-later
/*  KVM paravirtual clock driver. A clocksource implementation
    Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.
*/

#include <linux/clocksource.h>
#include <linux/kvm_para.h>
#include <asm/pvclock.h>
#include <asm/msr.h>
#include <asm/apic.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/cpuhotplug.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/set_memory.h>

#include <asm/hypervisor.h>
#include <asm/mem_encrypt.h>
#include <asm/x86_init.h>
#include <asm/reboot.h>
#include <asm/kvmclock.h>

static int kvmclock __initdata = 1;
static int kvmclock_vsyscall __initdata = 1;
static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
static u64 kvm_sched_clock_offset __ro_after_init;

static int __init parse_no_kvmclock(char *arg)
{
        kvmclock = 0;
        return 0;
}
early_param("no-kvmclock", parse_no_kvmclock);

static int __init parse_no_kvmclock_vsyscall(char *arg)
{
        kvmclock_vsyscall = 0;
        return 0;
}
early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);

/* Aligned to page sizes to match whats mapped via vsyscalls to userspace */
#define HV_CLOCK_SIZE   (sizeof(struct pvclock_vsyscall_time_info) * NR_CPUS)
#define HVC_BOOT_ARRAY_SIZE \
        (PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info))

static struct pvclock_vsyscall_time_info
                        hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
static struct pvclock_wall_clock wall_clock __bss_decrypted;
static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
static struct pvclock_vsyscall_time_info *hvclock_mem;

static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
{
        return &this_cpu_read(hv_clock_per_cpu)->pvti;
}

static inline struct pvclock_vsyscall_time_info *this_cpu_hvclock(void)
{
        return this_cpu_read(hv_clock_per_cpu);
}

/*
 * The wallclock is the time of day when we booted. Since then, some time may
 * have elapsed since the hypervisor wrote the data. So we try to account for
 * that with system time
 */
static void kvm_get_wallclock(struct timespec64 *now)
{
        wrmsrl(msr_kvm_wall_clock, slow_virt_to_phys(&wall_clock));
        preempt_disable();
        pvclock_read_wallclock(&wall_clock, this_cpu_pvti(), now);
        preempt_enable();
}

static int kvm_set_wallclock(const struct timespec64 *now)
{
        return -ENODEV;
}

static u64 kvm_clock_read(void)
{
        u64 ret;

        preempt_disable_notrace();
        ret = pvclock_clocksource_read(this_cpu_pvti());
        preempt_enable_notrace();
        return ret;
}

static u64 kvm_clock_get_cycles(struct clocksource *cs)
{
        return kvm_clock_read();
}

static u64 kvm_sched_clock_read(void)
{
        return kvm_clock_read() - kvm_sched_clock_offset;
}

static inline void kvm_sched_clock_init(bool stable)
{
        if (!stable)
                clear_sched_clock_stable();
        kvm_sched_clock_offset = kvm_clock_read();
        pv_ops.time.sched_clock = kvm_sched_clock_read;

        pr_info("kvm-clock: using sched offset of %llu cycles",
                kvm_sched_clock_offset);

        BUILD_BUG_ON(sizeof(kvm_sched_clock_offset) >
                sizeof(((struct pvclock_vcpu_time_info *)NULL)->system_time));
}

/*
 * If we don't do that, there is the possibility that the guest
 * will calibrate under heavy load - thus, getting a lower lpj -
 * and execute the delays themselves without load. This is wrong,
 * because no delay loop can finish beforehand.
 * Any heuristics is subject to fail, because ultimately, a large
 * poll of guests can be running and trouble each other. So we preset
 * lpj here
 */
static unsigned long kvm_get_tsc_khz(void)
{
        setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
        return pvclock_tsc_khz(this_cpu_pvti());
}

static void __init kvm_get_preset_lpj(void)
{
        unsigned long khz;
        u64 lpj;

        khz = kvm_get_tsc_khz();

        lpj = ((u64)khz * 1000);
        do_div(lpj, HZ);
        preset_lpj = lpj;
}

bool kvm_check_and_clear_guest_paused(void)
{
        struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
        bool ret = false;

        if (!src)
                return ret;

        if ((src->pvti.flags & PVCLOCK_GUEST_STOPPED) != 0) {
                src->pvti.flags &= ~PVCLOCK_GUEST_STOPPED;
                pvclock_touch_watchdogs();
                ret = true;
        }
        return ret;
}

struct clocksource kvm_clock = {
        .name   = "kvm-clock",
        .read   = kvm_clock_get_cycles,
        .rating = 400,
        .mask   = CLOCKSOURCE_MASK(64),
        .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
};
EXPORT_SYMBOL_GPL(kvm_clock);

static void kvm_register_clock(char *txt)
{
        struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
        u64 pa;

        if (!src)
                return;

        pa = slow_virt_to_phys(&src->pvti) | 0x01ULL;
        wrmsrl(msr_kvm_system_time, pa);
        pr_info("kvm-clock: cpu %d, msr %llx, %s", smp_processor_id(), pa, txt);
}

static void kvm_save_sched_clock_state(void)
{
}

static void kvm_restore_sched_clock_state(void)
{
        kvm_register_clock("primary cpu clock, resume");
}

#ifdef CONFIG_X86_LOCAL_APIC
static void kvm_setup_secondary_clock(void)
{
        kvm_register_clock("secondary cpu clock");
}
#endif

/*
 * After the clock is registered, the host will keep writing to the
 * registered memory location. If the guest happens to shutdown, this memory
 * won't be valid. In cases like kexec, in which you install a new kernel, this
 * means a random memory location will be kept being written. So before any
 * kind of shutdown from our side, we unregister the clock by writing anything
 * that does not have the 'enable' bit set in the msr
 */
#ifdef CONFIG_KEXEC_CORE
static void kvm_crash_shutdown(struct pt_regs *regs)
{
        native_write_msr(msr_kvm_system_time, 0, 0);
        kvm_disable_steal_time();
        native_machine_crash_shutdown(regs);
}
#endif

static void kvm_shutdown(void)
{
        native_write_msr(msr_kvm_system_time, 0, 0);
        kvm_disable_steal_time();
        native_machine_shutdown();
}

static void __init kvmclock_init_mem(void)
{
        unsigned long ncpus;
        unsigned int order;
        struct page *p;
        int r;

        if (HVC_BOOT_ARRAY_SIZE >= num_possible_cpus())
                return;

        ncpus = num_possible_cpus() - HVC_BOOT_ARRAY_SIZE;
        order = get_order(ncpus * sizeof(*hvclock_mem));

        p = alloc_pages(GFP_KERNEL, order);
        if (!p) {
                pr_warn("%s: failed to alloc %d pages", __func__, (1U << order));
                return;
        }

        hvclock_mem = page_address(p);

        /*
         * hvclock is shared between the guest and the hypervisor, must
         * be mapped decrypted.
         */
        if (sev_active()) {
                r = set_memory_decrypted((unsigned long) hvclock_mem,
                                         1UL << order);
                if (r) {
                        __free_pages(p, order);
                        hvclock_mem = NULL;
                        pr_warn("kvmclock: set_memory_decrypted() failed. Disabling\n");
                        return;
                }
        }

        memset(hvclock_mem, 0, PAGE_SIZE << order);
}

static int __init kvm_setup_vsyscall_timeinfo(void)
{
#ifdef CONFIG_X86_64
        u8 flags;

        if (!per_cpu(hv_clock_per_cpu, 0) || !kvmclock_vsyscall)
                return 0;

        flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
        if (!(flags & PVCLOCK_TSC_STABLE_BIT))
                return 0;

        kvm_clock.archdata.vclock_mode = VCLOCK_PVCLOCK;
#endif

        kvmclock_init_mem();

        return 0;
}
early_initcall(kvm_setup_vsyscall_timeinfo);

static int kvmclock_setup_percpu(unsigned int cpu)
{
        struct pvclock_vsyscall_time_info *p = per_cpu(hv_clock_per_cpu, cpu);

        /*
         * The per cpu area setup replicates CPU0 data to all cpu
         * pointers. So carefully check. CPU0 has been set up in init
         * already.
         */
        if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
                return 0;

        /* Use the static page for the first CPUs, allocate otherwise */
        if (cpu < HVC_BOOT_ARRAY_SIZE)
                p = &hv_clock_boot[cpu];
        else if (hvclock_mem)
                p = hvclock_mem + cpu - HVC_BOOT_ARRAY_SIZE;
        else
                return -ENOMEM;

        per_cpu(hv_clock_per_cpu, cpu) = p;
        return p ? 0 : -ENOMEM;
}

void __init kvmclock_init(void)
{
        u8 flags;

        if (!kvm_para_available() || !kvmclock)
                return;

        if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
                msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
                msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
        } else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
                return;
        }

        if (cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu",
                              kvmclock_setup_percpu, NULL) < 0) {
                return;
        }

        pr_info("kvm-clock: Using msrs %x and %x",
                msr_kvm_system_time, msr_kvm_wall_clock);

        this_cpu_write(hv_clock_per_cpu, &hv_clock_boot[0]);
        kvm_register_clock("primary cpu clock");
        pvclock_set_pvti_cpu0_va(hv_clock_boot);

        if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
                pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);

        flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
        kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);

        x86_platform.calibrate_tsc = kvm_get_tsc_khz;
        x86_platform.calibrate_cpu = kvm_get_tsc_khz;
        x86_platform.get_wallclock = kvm_get_wallclock;
        x86_platform.set_wallclock = kvm_set_wallclock;
#ifdef CONFIG_X86_LOCAL_APIC
        x86_cpuinit.early_percpu_clock_init = kvm_setup_secondary_clock;
#endif
        x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
        x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
        machine_ops.shutdown  = kvm_shutdown;
#ifdef CONFIG_KEXEC_CORE
        machine_ops.crash_shutdown  = kvm_crash_shutdown;
#endif
        kvm_get_preset_lpj();

        /*
         * X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
         * with P/T states and does not stop in deep C-states.
         *
         * Invariant TSC exposed by host means kvmclock is not necessary:
         * can use TSC as clocksource.
         *
         */
        if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
            boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
            !check_tsc_unstable())
                kvm_clock.rating = 299;

        clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
        pv_info.name = "KVM";
}