// SPDX-License-Identifier: GPL-2.0-only
/*
 * BTS PMU driver for perf
 * Copyright (c) 2013-2014, Intel Corporation.
 */

#undef DEBUG

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/bitops.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/coredump.h>

#include <linux/sizes.h>
#include <asm/perf_event.h>

#include "../perf_event.h"

struct bts_ctx {
        struct perf_output_handle       handle;
        struct debug_store              ds_back;
        int                             state;
};

/* BTS context states: */
enum {
        /* no ongoing AUX transactions */
        BTS_STATE_STOPPED = 0,
        /* AUX transaction is on, BTS tracing is disabled */
        BTS_STATE_INACTIVE,
        /* AUX transaction is on, BTS tracing is running */
        BTS_STATE_ACTIVE,
};

static DEFINE_PER_CPU(struct bts_ctx, bts_ctx);

#define BTS_RECORD_SIZE         24
#define BTS_SAFETY_MARGIN       4080

struct bts_phys {
        struct page     *page;
        unsigned long   size;
        unsigned long   offset;
        unsigned long   displacement;
};

struct bts_buffer {
        size_t          real_size;      /* multiple of BTS_RECORD_SIZE */
        unsigned int    nr_pages;
        unsigned int    nr_bufs;
        unsigned int    cur_buf;
        bool            snapshot;
        local_t         data_size;
        local_t         head;
        unsigned long   end;
        void            **data_pages;
        struct bts_phys buf[0];
};

static struct pmu bts_pmu;

static int buf_nr_pages(struct page *page)
{
        if (!PagePrivate(page))
                return 1;

        return 1 << page_private(page);
}

static size_t buf_size(struct page *page)
{
        return buf_nr_pages(page) * PAGE_SIZE;
}

static void *
bts_buffer_setup_aux(struct perf_event *event, void **pages,
                     int nr_pages, bool overwrite)
{
        struct bts_buffer *buf;
        struct page *page;
        int cpu = event->cpu;
        int node = (cpu == -1) ? cpu : cpu_to_node(cpu);
        unsigned long offset;
        size_t size = nr_pages << PAGE_SHIFT;
        int pg, nbuf, pad;

        /* count all the high order buffers */
        for (pg = 0, nbuf = 0; pg < nr_pages;) {
                page = virt_to_page(pages[pg]);
                pg += buf_nr_pages(page);
                nbuf++;
        }

        /*
         * to avoid interrupts in overwrite mode, only allow one physical
         */
        if (overwrite && nbuf > 1)
                return NULL;

        buf = kzalloc_node(offsetof(struct bts_buffer, buf[nbuf]), GFP_KERNEL, node);
        if (!buf)
                return NULL;

        buf->nr_pages = nr_pages;
        buf->nr_bufs = nbuf;
        buf->snapshot = overwrite;
        buf->data_pages = pages;
        buf->real_size = size - size % BTS_RECORD_SIZE;

        for (pg = 0, nbuf = 0, offset = 0, pad = 0; nbuf < buf->nr_bufs; nbuf++) {
                unsigned int __nr_pages;

                page = virt_to_page(pages[pg]);
                __nr_pages = buf_nr_pages(page);
                buf->buf[nbuf].page = page;
                buf->buf[nbuf].offset = offset;
                buf->buf[nbuf].displacement = (pad ? BTS_RECORD_SIZE - pad : 0);
                buf->buf[nbuf].size = buf_size(page) - buf->buf[nbuf].displacement;
                pad = buf->buf[nbuf].size % BTS_RECORD_SIZE;
                buf->buf[nbuf].size -= pad;

                pg += __nr_pages;
                offset += __nr_pages << PAGE_SHIFT;
        }

        return buf;
}

static void bts_buffer_free_aux(void *data)
{
        kfree(data);
}

static unsigned long bts_buffer_offset(struct bts_buffer *buf, unsigned int idx)
{
        return buf->buf[idx].offset + buf->buf[idx].displacement;
}

static void
bts_config_buffer(struct bts_buffer *buf)
{
        int cpu = raw_smp_processor_id();
        struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
        struct bts_phys *phys = &buf->buf[buf->cur_buf];
        unsigned long index, thresh = 0, end = phys->size;
        struct page *page = phys->page;

        index = local_read(&buf->head);

        if (!buf->snapshot) {
                if (buf->end < phys->offset + buf_size(page))
                        end = buf->end - phys->offset - phys->displacement;

                index -= phys->offset + phys->displacement;

                if (end - index > BTS_SAFETY_MARGIN)
                        thresh = end - BTS_SAFETY_MARGIN;
                else if (end - index > BTS_RECORD_SIZE)
                        thresh = end - BTS_RECORD_SIZE;
                else
                        thresh = end;
        }

        ds->bts_buffer_base = (u64)(long)page_address(page) + phys->displacement;
        ds->bts_index = ds->bts_buffer_base + index;
        ds->bts_absolute_maximum = ds->bts_buffer_base + end;
        ds->bts_interrupt_threshold = !buf->snapshot
                ? ds->bts_buffer_base + thresh
                : ds->bts_absolute_maximum + BTS_RECORD_SIZE;
}

static void bts_buffer_pad_out(struct bts_phys *phys, unsigned long head)
{
        unsigned long index = head - phys->offset;

        memset(page_address(phys->page) + index, 0, phys->size - index);
}

static void bts_update(struct bts_ctx *bts)
{
        int cpu = raw_smp_processor_id();
        struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
        struct bts_buffer *buf = perf_get_aux(&bts->handle);
        unsigned long index = ds->bts_index - ds->bts_buffer_base, old, head;

        if (!buf)
                return;

        head = index + bts_buffer_offset(buf, buf->cur_buf);
        old = local_xchg(&buf->head, head);

        if (!buf->snapshot) {
                if (old == head)
                        return;

                if (ds->bts_index >= ds->bts_absolute_maximum)
                        perf_aux_output_flag(&bts->handle,
                                             PERF_AUX_FLAG_TRUNCATED);

                /*
                 * old and head are always in the same physical buffer, so we
                 * can subtract them to get the data size.
                 */
                local_add(head - old, &buf->data_size);
        } else {
                local_set(&buf->data_size, head);
        }
}

static int
bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle);

/*
 * Ordering PMU callbacks wrt themselves and the PMI is done by means
 * of bts::state, which:
 *  - is set when bts::handle::event is valid, that is, between
 *    perf_aux_output_begin() and perf_aux_output_end();
 *  - is zero otherwise;
 *  - is ordered against bts::handle::event with a compiler barrier.
 */

static void __bts_event_start(struct perf_event *event)
{
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
        struct bts_buffer *buf = perf_get_aux(&bts->handle);
        u64 config = 0;

        if (!buf->snapshot)
                config |= ARCH_PERFMON_EVENTSEL_INT;
        if (!event->attr.exclude_kernel)
                config |= ARCH_PERFMON_EVENTSEL_OS;
        if (!event->attr.exclude_user)
                config |= ARCH_PERFMON_EVENTSEL_USR;

        bts_config_buffer(buf);

        /*
         * local barrier to make sure that ds configuration made it
         * before we enable BTS and bts::state goes ACTIVE
         */
        wmb();

        /* INACTIVE/STOPPED -> ACTIVE */
        WRITE_ONCE(bts->state, BTS_STATE_ACTIVE);

        intel_pmu_enable_bts(config);

}

static void bts_event_start(struct perf_event *event, int flags)
{
        struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
        struct bts_buffer *buf;

        buf = perf_aux_output_begin(&bts->handle, event);
        if (!buf)
                goto fail_stop;

        if (bts_buffer_reset(buf, &bts->handle))
                goto fail_end_stop;

        bts->ds_back.bts_buffer_base = cpuc->ds->bts_buffer_base;
        bts->ds_back.bts_absolute_maximum = cpuc->ds->bts_absolute_maximum;
        bts->ds_back.bts_interrupt_threshold = cpuc->ds->bts_interrupt_threshold;

        perf_event_itrace_started(event);
        event->hw.state = 0;

        __bts_event_start(event);

        return;

fail_end_stop:
        perf_aux_output_end(&bts->handle, 0);

fail_stop:
        event->hw.state = PERF_HES_STOPPED;
}

static void __bts_event_stop(struct perf_event *event, int state)
{
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);

        /* ACTIVE -> INACTIVE(PMI)/STOPPED(->stop()) */
        WRITE_ONCE(bts->state, state);

        /*
         * No extra synchronization is mandated by the documentation to have
         * BTS data stores globally visible.
         */
        intel_pmu_disable_bts();
}

static void bts_event_stop(struct perf_event *event, int flags)
{
        struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
        struct bts_buffer *buf = NULL;
        int state = READ_ONCE(bts->state);

        if (state == BTS_STATE_ACTIVE)
                __bts_event_stop(event, BTS_STATE_STOPPED);

        if (state != BTS_STATE_STOPPED)
                buf = perf_get_aux(&bts->handle);

        event->hw.state |= PERF_HES_STOPPED;

        if (flags & PERF_EF_UPDATE) {
                bts_update(bts);

                if (buf) {
                        if (buf->snapshot)
                                bts->handle.head =
                                        local_xchg(&buf->data_size,
                                                   buf->nr_pages << PAGE_SHIFT);
                        perf_aux_output_end(&bts->handle,
                                            local_xchg(&buf->data_size, 0));
                }

                cpuc->ds->bts_index = bts->ds_back.bts_buffer_base;
                cpuc->ds->bts_buffer_base = bts->ds_back.bts_buffer_base;
                cpuc->ds->bts_absolute_maximum = bts->ds_back.bts_absolute_maximum;
                cpuc->ds->bts_interrupt_threshold = bts->ds_back.bts_interrupt_threshold;
        }
}

void intel_bts_enable_local(void)
{
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
        int state = READ_ONCE(bts->state);

        /*
         * Here we transition from INACTIVE to ACTIVE;
         * if we instead are STOPPED from the interrupt handler,
         * stay that way. Can't be ACTIVE here though.
         */
        if (WARN_ON_ONCE(state == BTS_STATE_ACTIVE))
                return;

        if (state == BTS_STATE_STOPPED)
                return;

        if (bts->handle.event)
                __bts_event_start(bts->handle.event);
}

void intel_bts_disable_local(void)
{
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);

        /*
         * Here we transition from ACTIVE to INACTIVE;
         * do nothing for STOPPED or INACTIVE.
         */
        if (READ_ONCE(bts->state) != BTS_STATE_ACTIVE)
                return;

        if (bts->handle.event)
                __bts_event_stop(bts->handle.event, BTS_STATE_INACTIVE);
}

static int
bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle)
{
        unsigned long head, space, next_space, pad, gap, skip, wakeup;
        unsigned int next_buf;
        struct bts_phys *phys, *next_phys;
        int ret;

        if (buf->snapshot)
                return 0;

        head = handle->head & ((buf->nr_pages << PAGE_SHIFT) - 1);

        phys = &buf->buf[buf->cur_buf];
        space = phys->offset + phys->displacement + phys->size - head;
        pad = space;
        if (space > handle->size) {
                space = handle->size;
                space -= space % BTS_RECORD_SIZE;
        }
        if (space <= BTS_SAFETY_MARGIN) {
                /* See if next phys buffer has more space */
                next_buf = buf->cur_buf + 1;
                if (next_buf >= buf->nr_bufs)
                        next_buf = 0;
                next_phys = &buf->buf[next_buf];
                gap = buf_size(phys->page) - phys->displacement - phys->size +
                      next_phys->displacement;
                skip = pad + gap;
                if (handle->size >= skip) {
                        next_space = next_phys->size;
                        if (next_space + skip > handle->size) {
                                next_space = handle->size - skip;
                                next_space -= next_space % BTS_RECORD_SIZE;
                        }
                        if (next_space > space || !space) {
                                if (pad)
                                        bts_buffer_pad_out(phys, head);
                                ret = perf_aux_output_skip(handle, skip);
                                if (ret)
                                        return ret;
                                /* Advance to next phys buffer */
                                phys = next_phys;
                                space = next_space;
                                head = phys->offset + phys->displacement;
                                /*
                                 * After this, cur_buf and head won't match ds
                                 * anymore, so we must not be racing with
                                 * bts_update().
                                 */
                                buf->cur_buf = next_buf;
                                local_set(&buf->head, head);
                        }
                }
        }

        /* Don't go far beyond wakeup watermark */
        wakeup = BTS_SAFETY_MARGIN + BTS_RECORD_SIZE + handle->wakeup -
                 handle->head;
        if (space > wakeup) {
                space = wakeup;
                space -= space % BTS_RECORD_SIZE;
        }

        buf->end = head + space;

        /*
         * If we have no space, the lost notification would have been sent when
         * we hit absolute_maximum - see bts_update()
         */
        if (!space)
                return -ENOSPC;

        return 0;
}

int intel_bts_interrupt(void)
{
        struct debug_store *ds = this_cpu_ptr(&cpu_hw_events)->ds;
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
        struct perf_event *event = bts->handle.event;
        struct bts_buffer *buf;
        s64 old_head;
        int err = -ENOSPC, handled = 0;

        /*
         * The only surefire way of knowing if this NMI is ours is by checking
         * the write ptr against the PMI threshold.
         */
        if (ds && (ds->bts_index >= ds->bts_interrupt_threshold))
                handled = 1;

        /*
         * this is wrapped in intel_bts_enable_local/intel_bts_disable_local,
         * so we can only be INACTIVE or STOPPED
         */
        if (READ_ONCE(bts->state) == BTS_STATE_STOPPED)
                return handled;

        buf = perf_get_aux(&bts->handle);
        if (!buf)
                return handled;

        /*
         * Skip snapshot counters: they don't use the interrupt, but
         * there's no other way of telling, because the pointer will
         * keep moving
         */
        if (buf->snapshot)
                return 0;

        old_head = local_read(&buf->head);
        bts_update(bts);

        /* no new data */
        if (old_head == local_read(&buf->head))
                return handled;

        perf_aux_output_end(&bts->handle, local_xchg(&buf->data_size, 0));

        buf = perf_aux_output_begin(&bts->handle, event);
        if (buf)
                err = bts_buffer_reset(buf, &bts->handle);

        if (err) {
                WRITE_ONCE(bts->state, BTS_STATE_STOPPED);

                if (buf) {
                        /*
                         * BTS_STATE_STOPPED should be visible before
                         * cleared handle::event
                         */
                        barrier();
                        perf_aux_output_end(&bts->handle, 0);
                }
        }

        return 1;
}

static void bts_event_del(struct perf_event *event, int mode)
{
        bts_event_stop(event, PERF_EF_UPDATE);
}

static int bts_event_add(struct perf_event *event, int mode)
{
        struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
        struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
        struct hw_perf_event *hwc = &event->hw;

        event->hw.state = PERF_HES_STOPPED;

        if (test_bit(INTEL_PMC_IDX_FIXED_BTS, cpuc->active_mask))
                return -EBUSY;

        if (bts->handle.event)
                return -EBUSY;

        if (mode & PERF_EF_START) {
                bts_event_start(event, 0);
                if (hwc->state & PERF_HES_STOPPED)
                        return -EINVAL;
        }

        return 0;
}

static void bts_event_destroy(struct perf_event *event)
{
        x86_release_hardware();
        x86_del_exclusive(x86_lbr_exclusive_bts);
}

static int bts_event_init(struct perf_event *event)
{
        int ret;

        if (event->attr.type != bts_pmu.type)
                return -ENOENT;

        /*
         * BTS leaks kernel addresses even when CPL0 tracing is
         * disabled, so disallow intel_bts driver for unprivileged
         * users on paranoid systems since it provides trace data
         * to the user in a zero-copy fashion.
         *
         * Note that the default paranoia setting permits unprivileged
         * users to profile the kernel.
         */
        if (event->attr.exclude_kernel) {
                ret = perf_allow_kernel(&event->attr);
                if (ret)
                        return ret;
        }

        if (x86_add_exclusive(x86_lbr_exclusive_bts))
                return -EBUSY;

        ret = x86_reserve_hardware();
        if (ret) {
                x86_del_exclusive(x86_lbr_exclusive_bts);
                return ret;
        }

        event->destroy = bts_event_destroy;

        return 0;
}

static void bts_event_read(struct perf_event *event)
{
}

static __init int bts_init(void)
{
        if (!boot_cpu_has(X86_FEATURE_DTES64) || !x86_pmu.bts)
                return -ENODEV;

        if (boot_cpu_has(X86_FEATURE_PTI)) {
                /*
                 * BTS hardware writes through a virtual memory map we must
                 * either use the kernel physical map, or the user mapping of
                 * the AUX buffer.
                 *
                 * However, since this driver supports per-CPU and per-task inherit
                 * we cannot use the user mapping since it will not be available
                 * if we're not running the owning process.
                 *
                 * With PTI we can't use the kernal map either, because its not
                 * there when we run userspace.
                 *
                 * For now, disable this driver when using PTI.
                 */
                return -ENODEV;
        }

        bts_pmu.capabilities    = PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE |
                                  PERF_PMU_CAP_EXCLUSIVE;
        bts_pmu.task_ctx_nr     = perf_sw_context;
        bts_pmu.event_init      = bts_event_init;
        bts_pmu.add             = bts_event_add;
        bts_pmu.del             = bts_event_del;
        bts_pmu.start           = bts_event_start;
        bts_pmu.stop            = bts_event_stop;
        bts_pmu.read            = bts_event_read;
        bts_pmu.setup_aux       = bts_buffer_setup_aux;
        bts_pmu.free_aux        = bts_buffer_free_aux;

        return perf_pmu_register(&bts_pmu, "intel_bts", -1);
}
arch_initcall(bts_init);