/*
 * Performance events ring-buffer code:
 *
 *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
 *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
 *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
 *
 * For licensing details see kernel-base/COPYING
 */

#include <linux/perf_event.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/circ_buf.h>
#include <linux/poll.h>

#include "internal.h"

static void perf_output_wakeup(struct perf_output_handle *handle)
{
        atomic_set(&handle->rb->poll, POLLIN);

        handle->event->pending_wakeup = 1;
        irq_work_queue(&handle->event->pending);
}

/*
 * We need to ensure a later event_id doesn't publish a head when a former
 * event isn't done writing. However since we need to deal with NMIs we
 * cannot fully serialize things.
 *
 * We only publish the head (and generate a wakeup) when the outer-most
 * event completes.
 */
static void perf_output_get_handle(struct perf_output_handle *handle)
{
        struct ring_buffer *rb = handle->rb;

        preempt_disable();
        local_inc(&rb->nest);
        handle->wakeup = local_read(&rb->wakeup);
}

static void perf_output_put_handle(struct perf_output_handle *handle)
{
        struct ring_buffer *rb = handle->rb;
        unsigned long head;

again:
        head = local_read(&rb->head);

        /*
         * IRQ/NMI can happen here, which means we can miss a head update.
         */

        if (!local_dec_and_test(&rb->nest))
                goto out;

        /*
         * Since the mmap() consumer (userspace) can run on a different CPU:
         *
         *   kernel                             user
         *
         *   if (LOAD ->data_tail) {            LOAD ->data_head
         *                      (A)             smp_rmb()       (C)
         *      STORE $data                     LOAD $data
         *      smp_wmb()       (B)             smp_mb()        (D)
         *      STORE ->data_head               STORE ->data_tail
         *   }
         *
         * Where A pairs with D, and B pairs with C.
         *
         * In our case (A) is a control dependency that separates the load of
         * the ->data_tail and the stores of $data. In case ->data_tail
         * indicates there is no room in the buffer to store $data we do not.
         *
         * D needs to be a full barrier since it separates the data READ
         * from the tail WRITE.
         *
         * For B a WMB is sufficient since it separates two WRITEs, and for C
         * an RMB is sufficient since it separates two READs.
         *
         * See perf_output_begin().
         */
        smp_wmb(); /* B, matches C */
        rb->user_page->data_head = head;

        /*
         * Now check if we missed an update -- rely on previous implied
         * compiler barriers to force a re-read.
         */
        if (unlikely(head != local_read(&rb->head))) {
                local_inc(&rb->nest);
                goto again;
        }

        if (handle->wakeup != local_read(&rb->wakeup))
                perf_output_wakeup(handle);

out:
        preempt_enable();
}

int perf_output_begin(struct perf_output_handle *handle,
                      struct perf_event *event, unsigned int size)
{
        struct ring_buffer *rb;
        unsigned long tail, offset, head;
        int have_lost, page_shift;
        struct {
                struct perf_event_header header;
                u64                      id;
                u64                      lost;
        } lost_event;

        rcu_read_lock();
        /*
         * For inherited events we send all the output towards the parent.
         */
        if (event->parent)
                event = event->parent;

        rb = rcu_dereference(event->rb);
        if (unlikely(!rb))
                goto out;

        if (unlikely(!rb->nr_pages))
                goto out;

        handle->rb    = rb;
        handle->event = event;

        have_lost = local_read(&rb->lost);
        if (unlikely(have_lost)) {
                size += sizeof(lost_event);
                if (event->attr.sample_id_all)
                        size += event->id_header_size;
        }

        perf_output_get_handle(handle);

        do {
                tail = ACCESS_ONCE(rb->user_page->data_tail);
                offset = head = local_read(&rb->head);
                if (!rb->overwrite &&
                    unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
                        goto fail;

                /*
                 * The above forms a control dependency barrier separating the
                 * @tail load above from the data stores below. Since the @tail
                 * load is required to compute the branch to fail below.
                 *
                 * A, matches D; the full memory barrier userspace SHOULD issue
                 * after reading the data and before storing the new tail
                 * position.
                 *
                 * See perf_output_put_handle().
                 */

                head += size;
        } while (local_cmpxchg(&rb->head, offset, head) != offset);

        /*
         * We rely on the implied barrier() by local_cmpxchg() to ensure
         * none of the data stores below can be lifted up by the compiler.
         */

        if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
                local_add(rb->watermark, &rb->wakeup);

        page_shift = PAGE_SHIFT + page_order(rb);

        handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
        offset &= (1UL << page_shift) - 1;
        handle->addr = rb->data_pages[handle->page] + offset;
        handle->size = (1UL << page_shift) - offset;

        if (unlikely(have_lost)) {
                struct perf_sample_data sample_data;

                lost_event.header.size = sizeof(lost_event);
                lost_event.header.type = PERF_RECORD_LOST;
                lost_event.header.misc = 0;
                lost_event.id          = event->id;
                lost_event.lost        = local_xchg(&rb->lost, 0);

                perf_event_header__init_id(&lost_event.header,
                                           &sample_data, event);
                perf_output_put(handle, lost_event);
                perf_event__output_id_sample(event, handle, &sample_data);
        }

        return 0;

fail:
        local_inc(&rb->lost);
        perf_output_put_handle(handle);
out:
        rcu_read_unlock();

        return -ENOSPC;
}

unsigned int perf_output_copy(struct perf_output_handle *handle,
                      const void *buf, unsigned int len)
{
        return __output_copy(handle, buf, len);
}

unsigned int perf_output_skip(struct perf_output_handle *handle,
                              unsigned int len)
{
        return __output_skip(handle, NULL, len);
}

void perf_output_end(struct perf_output_handle *handle)
{
        perf_output_put_handle(handle);
        rcu_read_unlock();
}

static void
ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
{
        long max_size = perf_data_size(rb);

        if (watermark)
                rb->watermark = min(max_size, watermark);

        if (!rb->watermark)
                rb->watermark = max_size / 2;

        if (flags & RING_BUFFER_WRITABLE)
                rb->overwrite = 0;
        else
                rb->overwrite = 1;

        atomic_set(&rb->refcount, 1);

        INIT_LIST_HEAD(&rb->event_list);
        spin_lock_init(&rb->event_lock);
}

#ifndef CONFIG_PERF_USE_VMALLOC

/*
 * Back perf_mmap() with regular GFP_KERNEL-0 pages.
 */

struct page *
perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
{
        if (pgoff > rb->nr_pages)
                return NULL;

        if (pgoff == 0)
                return virt_to_page(rb->user_page);

        return virt_to_page(rb->data_pages[pgoff - 1]);
}

static void *perf_mmap_alloc_page(int cpu)
{
        struct page *page;
        int node;

        node = (cpu == -1) ? cpu : cpu_to_node(cpu);
        page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
        if (!page)
                return NULL;

        return page_address(page);
}

struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
{
        struct ring_buffer *rb;
        unsigned long size;
        int i;

        size = sizeof(struct ring_buffer);
        size += nr_pages * sizeof(void *);

        rb = kzalloc(size, GFP_KERNEL);
        if (!rb)
                goto fail;

        rb->user_page = perf_mmap_alloc_page(cpu);
        if (!rb->user_page)
                goto fail_user_page;

        for (i = 0; i < nr_pages; i++) {
                rb->data_pages[i] = perf_mmap_alloc_page(cpu);
                if (!rb->data_pages[i])
                        goto fail_data_pages;
        }

        rb->nr_pages = nr_pages;

        ring_buffer_init(rb, watermark, flags);

        return rb;

fail_data_pages:
        for (i--; i >= 0; i--)
                free_page((unsigned long)rb->data_pages[i]);

        free_page((unsigned long)rb->user_page);

fail_user_page:
        kfree(rb);

fail:
        return NULL;
}

static void perf_mmap_free_page(unsigned long addr)
{
        struct page *page = virt_to_page((void *)addr);

        page->mapping = NULL;
        __free_page(page);
}

void rb_free(struct ring_buffer *rb)
{
        int i;

        perf_mmap_free_page((unsigned long)rb->user_page);
        for (i = 0; i < rb->nr_pages; i++)
                perf_mmap_free_page((unsigned long)rb->data_pages[i]);
        kfree(rb);
}

#else
static int data_page_nr(struct ring_buffer *rb)
{
        return rb->nr_pages << page_order(rb);
}

struct page *
perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
{
        /* The '>' counts in the user page. */
        if (pgoff > data_page_nr(rb))
                return NULL;

        return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
}

static void perf_mmap_unmark_page(void *addr)
{
        struct page *page = vmalloc_to_page(addr);

        page->mapping = NULL;
}

static void rb_free_work(struct work_struct *work)
{
        struct ring_buffer *rb;
        void *base;
        int i, nr;

        rb = container_of(work, struct ring_buffer, work);
        nr = data_page_nr(rb);

        base = rb->user_page;
        /* The '<=' counts in the user page. */
        for (i = 0; i <= nr; i++)
                perf_mmap_unmark_page(base + (i * PAGE_SIZE));

        vfree(base);
        kfree(rb);
}

void rb_free(struct ring_buffer *rb)
{
        schedule_work(&rb->work);
}

struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
{
        struct ring_buffer *rb;
        unsigned long size;
        void *all_buf;

        size = sizeof(struct ring_buffer);
        size += sizeof(void *);

        rb = kzalloc(size, GFP_KERNEL);
        if (!rb)
                goto fail;

        INIT_WORK(&rb->work, rb_free_work);

        all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
        if (!all_buf)
                goto fail_all_buf;

        rb->user_page = all_buf;
        rb->data_pages[0] = all_buf + PAGE_SIZE;
        rb->page_order = ilog2(nr_pages);
        rb->nr_pages = !!nr_pages;

        ring_buffer_init(rb, watermark, flags);

        return rb;

fail_all_buf:
        kfree(rb);

fail:
        return NULL;
}

#endif