Merge tag 'trace-printf-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace...

[drm/drm-misc.git] / drivers / ptp / ptp_vmclock.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Virtual PTP 1588 clock for use with LM-safe VMclock device.
 *
 * Copyright © 2024 Amazon.com, Inc. or its affiliates.
 */

#include <linux/acpi.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#include <uapi/linux/vmclock-abi.h>

#include <linux/ptp_clock_kernel.h>

#ifdef CONFIG_X86
#include <asm/pvclock.h>
#include <asm/kvmclock.h>
#endif

#ifdef CONFIG_KVM_GUEST
#define SUPPORT_KVMCLOCK
#endif

static DEFINE_IDA(vmclock_ida);

ACPI_MODULE_NAME("vmclock");

struct vmclock_state {
        struct resource res;
        struct vmclock_abi *clk;
        struct miscdevice miscdev;
        struct ptp_clock_info ptp_clock_info;
        struct ptp_clock *ptp_clock;
        enum clocksource_ids cs_id, sys_cs_id;
        int index;
        char *name;
};

#define VMCLOCK_MAX_WAIT ms_to_ktime(100)

/* Require at least the flags field to be present. All else can be optional. */
#define VMCLOCK_MIN_SIZE offsetof(struct vmclock_abi, pad)

#define VMCLOCK_FIELD_PRESENT(_c, _f)                     \
        (le32_to_cpu((_c)->size) >= (offsetof(struct vmclock_abi, _f) + \
                                     sizeof((_c)->_f)))

/*
 * Multiply a 64-bit count by a 64-bit tick 'period' in units of seconds >> 64
 * and add the fractional second part of the reference time.
 *
 * The result is a 128-bit value, the top 64 bits of which are seconds, and
 * the low 64 bits are (seconds >> 64).
 */
static uint64_t mul_u64_u64_shr_add_u64(uint64_t *res_hi, uint64_t delta,
                                        uint64_t period, uint8_t shift,
                                        uint64_t frac_sec)
{
        unsigned __int128 res = (unsigned __int128)delta * period;

        res >>= shift;
        res += frac_sec;
        *res_hi = res >> 64;
        return (uint64_t)res;
}

static bool tai_adjust(struct vmclock_abi *clk, uint64_t *sec)
{
        if (likely(clk->time_type == VMCLOCK_TIME_UTC))
                return true;

        if (clk->time_type == VMCLOCK_TIME_TAI &&
            (le64_to_cpu(clk->flags) & VMCLOCK_FLAG_TAI_OFFSET_VALID)) {
                if (sec)
                        *sec += (int16_t)le16_to_cpu(clk->tai_offset_sec);
                return true;
        }
        return false;
}

static int vmclock_get_crosststamp(struct vmclock_state *st,
                                   struct ptp_system_timestamp *sts,
                                   struct system_counterval_t *system_counter,
                                   struct timespec64 *tspec)
{
        ktime_t deadline = ktime_add(ktime_get(), VMCLOCK_MAX_WAIT);
        struct system_time_snapshot systime_snapshot;
        uint64_t cycle, delta, seq, frac_sec;

#ifdef CONFIG_X86
        /*
         * We'd expect the hypervisor to know this and to report the clock
         * status as VMCLOCK_STATUS_UNRELIABLE. But be paranoid.
         */
        if (check_tsc_unstable())
                return -EINVAL;
#endif

        while (1) {
                seq = le32_to_cpu(st->clk->seq_count) & ~1ULL;

                /*
                 * This pairs with a write barrier in the hypervisor
                 * which populates this structure.
                 */
                virt_rmb();

                if (st->clk->clock_status == VMCLOCK_STATUS_UNRELIABLE)
                        return -EINVAL;

                /*
                 * When invoked for gettimex64(), fill in the pre/post system
                 * times. The simple case is when system time is based on the
                 * same counter as st->cs_id, in which case all three times
                 * will be derived from the *same* counter value.
                 *
                 * If the system isn't using the same counter, then the value
                 * from ktime_get_snapshot() will still be used as pre_ts, and
                 * ptp_read_system_postts() is called to populate postts after
                 * calling get_cycles().
                 *
                 * The conversion to timespec64 happens further down, outside
                 * the seq_count loop.
                 */
                if (sts) {
                        ktime_get_snapshot(&systime_snapshot);
                        if (systime_snapshot.cs_id == st->cs_id) {
                                cycle = systime_snapshot.cycles;
                        } else {
                                cycle = get_cycles();
                                ptp_read_system_postts(sts);
                        }
                } else {
                        cycle = get_cycles();
                }

                delta = cycle - le64_to_cpu(st->clk->counter_value);

                frac_sec = mul_u64_u64_shr_add_u64(&tspec->tv_sec, delta,
                                                   le64_to_cpu(st->clk->counter_period_frac_sec),
                                                   st->clk->counter_period_shift,
                                                   le64_to_cpu(st->clk->time_frac_sec));
                tspec->tv_nsec = mul_u64_u64_shr(frac_sec, NSEC_PER_SEC, 64);
                tspec->tv_sec += le64_to_cpu(st->clk->time_sec);

                if (!tai_adjust(st->clk, &tspec->tv_sec))
                        return -EINVAL;

                /*
                 * This pairs with a write barrier in the hypervisor
                 * which populates this structure.
                 */
                virt_rmb();
                if (seq == le32_to_cpu(st->clk->seq_count))
                        break;

                if (ktime_after(ktime_get(), deadline))
                        return -ETIMEDOUT;
        }

        if (system_counter) {
                system_counter->cycles = cycle;
                system_counter->cs_id = st->cs_id;
        }

        if (sts) {
                sts->pre_ts = ktime_to_timespec64(systime_snapshot.real);
                if (systime_snapshot.cs_id == st->cs_id)
                        sts->post_ts = sts->pre_ts;
        }

        return 0;
}

#ifdef SUPPORT_KVMCLOCK
/*
 * In the case where the system is using the KVM clock for timekeeping, convert
 * the TSC value into a KVM clock time in order to return a paired reading that
 * get_device_system_crosststamp() can cope with.
 */
static int vmclock_get_crosststamp_kvmclock(struct vmclock_state *st,
                                            struct ptp_system_timestamp *sts,
                                            struct system_counterval_t *system_counter,
                                            struct timespec64 *tspec)
{
        struct pvclock_vcpu_time_info *pvti = this_cpu_pvti();
        unsigned int pvti_ver;
        int ret;

        preempt_disable_notrace();

        do {
                pvti_ver = pvclock_read_begin(pvti);

                ret = vmclock_get_crosststamp(st, sts, system_counter, tspec);
                if (ret)
                        break;

                system_counter->cycles = __pvclock_read_cycles(pvti,
                                                               system_counter->cycles);
                system_counter->cs_id = CSID_X86_KVM_CLK;

                /*
                 * This retry should never really happen; if the TSC is
                 * stable and reliable enough across vCPUS that it is sane
                 * for the hypervisor to expose a VMCLOCK device which uses
                 * it as the reference counter, then the KVM clock sohuld be
                 * in 'master clock mode' and basically never changed. But
                 * the KVM clock is a fickle and often broken thing, so do
                 * it "properly" just in case.
                 */
        } while (pvclock_read_retry(pvti, pvti_ver));

        preempt_enable_notrace();

        return ret;
}
#endif

static int ptp_vmclock_get_time_fn(ktime_t *device_time,
                                   struct system_counterval_t *system_counter,
                                   void *ctx)
{
        struct vmclock_state *st = ctx;
        struct timespec64 tspec;
        int ret;

#ifdef SUPPORT_KVMCLOCK
        if (READ_ONCE(st->sys_cs_id) == CSID_X86_KVM_CLK)
                ret = vmclock_get_crosststamp_kvmclock(st, NULL, system_counter,
                                                       &tspec);
        else
#endif
                ret = vmclock_get_crosststamp(st, NULL, system_counter, &tspec);

        if (!ret)
                *device_time = timespec64_to_ktime(tspec);

        return ret;
}

static int ptp_vmclock_getcrosststamp(struct ptp_clock_info *ptp,
                                      struct system_device_crosststamp *xtstamp)
{
        struct vmclock_state *st = container_of(ptp, struct vmclock_state,
                                                ptp_clock_info);
        int ret = get_device_system_crosststamp(ptp_vmclock_get_time_fn, st,
                                                NULL, xtstamp);
#ifdef SUPPORT_KVMCLOCK
        /*
         * On x86, the KVM clock may be used for the system time. We can
         * actually convert a TSC reading to that, and return a paired
         * timestamp that get_device_system_crosststamp() *can* handle.
         */
        if (ret == -ENODEV) {
                struct system_time_snapshot systime_snapshot;

                ktime_get_snapshot(&systime_snapshot);

                if (systime_snapshot.cs_id == CSID_X86_TSC ||
                    systime_snapshot.cs_id == CSID_X86_KVM_CLK) {
                        WRITE_ONCE(st->sys_cs_id, systime_snapshot.cs_id);
                        ret = get_device_system_crosststamp(ptp_vmclock_get_time_fn,
                                                            st, NULL, xtstamp);
                }
        }
#endif
        return ret;
}

/*
 * PTP clock operations
 */

static int ptp_vmclock_adjfine(struct ptp_clock_info *ptp, long delta)
{
        return -EOPNOTSUPP;
}

static int ptp_vmclock_adjtime(struct ptp_clock_info *ptp, s64 delta)
{
        return -EOPNOTSUPP;
}

static int ptp_vmclock_settime(struct ptp_clock_info *ptp,
                           const struct timespec64 *ts)
{
        return -EOPNOTSUPP;
}

static int ptp_vmclock_gettimex(struct ptp_clock_info *ptp, struct timespec64 *ts,
                                struct ptp_system_timestamp *sts)
{
        struct vmclock_state *st = container_of(ptp, struct vmclock_state,
                                                ptp_clock_info);

        return vmclock_get_crosststamp(st, sts, NULL, ts);
}

static int ptp_vmclock_enable(struct ptp_clock_info *ptp,
                          struct ptp_clock_request *rq, int on)
{
        return -EOPNOTSUPP;
}

static const struct ptp_clock_info ptp_vmclock_info = {
        .owner          = THIS_MODULE,
        .max_adj        = 0,
        .n_ext_ts       = 0,
        .n_pins         = 0,
        .pps            = 0,
        .adjfine        = ptp_vmclock_adjfine,
        .adjtime        = ptp_vmclock_adjtime,
        .gettimex64     = ptp_vmclock_gettimex,
        .settime64      = ptp_vmclock_settime,
        .enable         = ptp_vmclock_enable,
        .getcrosststamp = ptp_vmclock_getcrosststamp,
};

static struct ptp_clock *vmclock_ptp_register(struct device *dev,
                                              struct vmclock_state *st)
{
        enum clocksource_ids cs_id;

        if (IS_ENABLED(CONFIG_ARM64) &&
            st->clk->counter_id == VMCLOCK_COUNTER_ARM_VCNT) {
                /* Can we check it's the virtual counter? */
                cs_id = CSID_ARM_ARCH_COUNTER;
        } else if (IS_ENABLED(CONFIG_X86) &&
                   st->clk->counter_id == VMCLOCK_COUNTER_X86_TSC) {
                cs_id = CSID_X86_TSC;
        } else {
                return NULL;
        }

        /* Only UTC, or TAI with offset */
        if (!tai_adjust(st->clk, NULL)) {
                dev_info(dev, "vmclock does not provide unambiguous UTC\n");
                return NULL;
        }

        st->sys_cs_id = cs_id;
        st->cs_id = cs_id;
        st->ptp_clock_info = ptp_vmclock_info;
        strscpy(st->ptp_clock_info.name, st->name);

        return ptp_clock_register(&st->ptp_clock_info, dev);
}

static int vmclock_miscdev_mmap(struct file *fp, struct vm_area_struct *vma)
{
        struct vmclock_state *st = container_of(fp->private_data,
                                                struct vmclock_state, miscdev);

        if ((vma->vm_flags & (VM_READ|VM_WRITE)) != VM_READ)
                return -EROFS;

        if (vma->vm_end - vma->vm_start != PAGE_SIZE || vma->vm_pgoff)
                return -EINVAL;

        if (io_remap_pfn_range(vma, vma->vm_start,
                               st->res.start >> PAGE_SHIFT, PAGE_SIZE,
                               vma->vm_page_prot))
                return -EAGAIN;

        return 0;
}

static ssize_t vmclock_miscdev_read(struct file *fp, char __user *buf,
                                    size_t count, loff_t *ppos)
{
        struct vmclock_state *st = container_of(fp->private_data,
                                                struct vmclock_state, miscdev);
        ktime_t deadline = ktime_add(ktime_get(), VMCLOCK_MAX_WAIT);
        size_t max_count;
        uint32_t seq;

        if (*ppos >= PAGE_SIZE)
                return 0;

        max_count = PAGE_SIZE - *ppos;
        if (count > max_count)
                count = max_count;

        while (1) {
                seq = le32_to_cpu(st->clk->seq_count) & ~1U;
                /* Pairs with hypervisor wmb */
                virt_rmb();

                if (copy_to_user(buf, ((char *)st->clk) + *ppos, count))
                        return -EFAULT;

                /* Pairs with hypervisor wmb */
                virt_rmb();
                if (seq == le32_to_cpu(st->clk->seq_count))
                        break;

                if (ktime_after(ktime_get(), deadline))
                        return -ETIMEDOUT;
        }

        *ppos += count;
        return count;
}

static const struct file_operations vmclock_miscdev_fops = {
        .mmap = vmclock_miscdev_mmap,
        .read = vmclock_miscdev_read,
};

/* module operations */

static void vmclock_remove(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct vmclock_state *st = dev_get_drvdata(dev);

        if (st->ptp_clock)
                ptp_clock_unregister(st->ptp_clock);

        if (st->miscdev.minor != MISC_DYNAMIC_MINOR)
                misc_deregister(&st->miscdev);
}

static acpi_status vmclock_acpi_resources(struct acpi_resource *ares, void *data)
{
        struct vmclock_state *st = data;
        struct resource_win win;
        struct resource *res = &win.res;

        if (ares->type == ACPI_RESOURCE_TYPE_END_TAG)
                return AE_OK;

        /* There can be only one */
        if (resource_type(&st->res) == IORESOURCE_MEM)
                return AE_ERROR;

        if (acpi_dev_resource_memory(ares, res) ||
            acpi_dev_resource_address_space(ares, &win)) {

                if (resource_type(res) != IORESOURCE_MEM ||
                    resource_size(res) < sizeof(st->clk))
                        return AE_ERROR;

                st->res = *res;
                return AE_OK;
        }

        return AE_ERROR;
}

static int vmclock_probe_acpi(struct device *dev, struct vmclock_state *st)
{
        struct acpi_device *adev = ACPI_COMPANION(dev);
        acpi_status status;

        /*
         * This should never happen as this function is only called when
         * has_acpi_companion(dev) is true, but the logic is sufficiently
         * complex that Coverity can't see the tautology.
         */
        if (!adev)
                return -ENODEV;

        status = acpi_walk_resources(adev->handle, METHOD_NAME__CRS,
                                     vmclock_acpi_resources, st);
        if (ACPI_FAILURE(status) || resource_type(&st->res) != IORESOURCE_MEM) {
                dev_err(dev, "failed to get resources\n");
                return -ENODEV;
        }

        return 0;
}

static void vmclock_put_idx(void *data)
{
        struct vmclock_state *st = data;

        ida_free(&vmclock_ida, st->index);
}

static int vmclock_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct vmclock_state *st;
        int ret;

        st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
        if (!st)
                return -ENOMEM;

        if (has_acpi_companion(dev))
                ret = vmclock_probe_acpi(dev, st);
        else
                ret = -EINVAL; /* Only ACPI for now */

        if (ret) {
                dev_info(dev, "Failed to obtain physical address: %d\n", ret);
                goto out;
        }

        if (resource_size(&st->res) < VMCLOCK_MIN_SIZE) {
                dev_info(dev, "Region too small (0x%llx)\n",
                         resource_size(&st->res));
                ret = -EINVAL;
                goto out;
        }
        st->clk = devm_memremap(dev, st->res.start, resource_size(&st->res),
                                MEMREMAP_WB | MEMREMAP_DEC);
        if (IS_ERR(st->clk)) {
                ret = PTR_ERR(st->clk);
                dev_info(dev, "failed to map shared memory\n");
                st->clk = NULL;
                goto out;
        }

        if (le32_to_cpu(st->clk->magic) != VMCLOCK_MAGIC ||
            le32_to_cpu(st->clk->size) > resource_size(&st->res) ||
            le16_to_cpu(st->clk->version) != 1) {
                dev_info(dev, "vmclock magic fields invalid\n");
                ret = -EINVAL;
                goto out;
        }

        ret = ida_alloc(&vmclock_ida, GFP_KERNEL);
        if (ret < 0)
                goto out;

        st->index = ret;
        ret = devm_add_action_or_reset(&pdev->dev, vmclock_put_idx, st);
        if (ret)
                goto out;

        st->name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "vmclock%d", st->index);
        if (!st->name) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * If the structure is big enough, it can be mapped to userspace.
         * Theoretically a guest OS even using larger pages could still
         * use 4KiB PTEs to map smaller MMIO regions like this, but let's
         * cross that bridge if/when we come to it.
         */
        if (le32_to_cpu(st->clk->size) >= PAGE_SIZE) {
                st->miscdev.minor = MISC_DYNAMIC_MINOR;
                st->miscdev.fops = &vmclock_miscdev_fops;
                st->miscdev.name = st->name;

                ret = misc_register(&st->miscdev);
                if (ret)
                        goto out;
        }

        /* If there is valid clock information, register a PTP clock */
        if (VMCLOCK_FIELD_PRESENT(st->clk, time_frac_sec)) {
                /* Can return a silent NULL, or an error. */
                st->ptp_clock = vmclock_ptp_register(dev, st);
                if (IS_ERR(st->ptp_clock)) {
                        ret = PTR_ERR(st->ptp_clock);
                        st->ptp_clock = NULL;
                        vmclock_remove(pdev);
                        goto out;
                }
        }

        if (!st->miscdev.minor && !st->ptp_clock) {
                /* Neither miscdev nor PTP registered */
                dev_info(dev, "vmclock: Neither miscdev nor PTP available; not registering\n");
                ret = -ENODEV;
                goto out;
        }

        dev_info(dev, "%s: registered %s%s%s\n", st->name,
                 st->miscdev.minor ? "miscdev" : "",
                 (st->miscdev.minor && st->ptp_clock) ? ", " : "",
                 st->ptp_clock ? "PTP" : "");

        dev_set_drvdata(dev, st);

 out:
        return ret;
}

static const struct acpi_device_id vmclock_acpi_ids[] = {
        { "AMZNC10C", 0 },
        {}
};
MODULE_DEVICE_TABLE(acpi, vmclock_acpi_ids);

static struct platform_driver vmclock_platform_driver = {
        .probe          = vmclock_probe,
        .remove_new     = vmclock_remove,
        .driver = {
                .name   = "vmclock",
                .acpi_match_table = vmclock_acpi_ids,
        },
};

module_platform_driver(vmclock_platform_driver)

MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
MODULE_DESCRIPTION("PTP clock using VMCLOCK");
MODULE_LICENSE("GPL");