perf/ring_buffer: Fix exposing a temporarily decreased data_head

[thirdparty/kernel/stable.git] / kernel / events / ring_buffer.c

/*
 * 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
 *  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 <linux/nospec.h>

#include "internal.h"

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

        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 and advance @rb->head, causing our
         * load above to be stale.
         */

        /*
         * If this isn't the outermost nesting, we don't have to update
         * @rb->user_page->data_head.
         */
        if (local_read(&rb->nest) > 1) {
                local_dec(&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;

        /*
         * We must publish the head before decrementing the nest count,
         * otherwise an IRQ/NMI can publish a more recent head value and our
         * write will (temporarily) publish a stale value.
         */
        barrier();
        local_set(&rb->nest, 0);

        /*
         * Ensure we decrement @rb->nest before we validate the @rb->head.
         * Otherwise we cannot be sure we caught the 'last' nested update.
         */
        barrier();
        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();
}

static __always_inline bool
ring_buffer_has_space(unsigned long head, unsigned long tail,
                      unsigned long data_size, unsigned int size,
                      bool backward)
{
        if (!backward)
                return CIRC_SPACE(head, tail, data_size) >= size;
        else
                return CIRC_SPACE(tail, head, data_size) >= size;
}

static __always_inline int
__perf_output_begin(struct perf_output_handle *handle,
                    struct perf_event *event, unsigned int size,
                    bool backward)
{
        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->paused)) {
                if (rb->nr_pages)
                        local_inc(&rb->lost);
                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 = READ_ONCE(rb->user_page->data_tail);
                offset = head = local_read(&rb->head);
                if (!rb->overwrite) {
                        if (unlikely(!ring_buffer_has_space(head, tail,
                                                            perf_data_size(rb),
                                                            size, backward)))
                                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().
                 */

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

        if (backward) {
                offset = head;
                head = (u64)(-head);
        }

        /*
         * 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;
}

int perf_output_begin_forward(struct perf_output_handle *handle,
                             struct perf_event *event, unsigned int size)
{
        return __perf_output_begin(handle, event, size, false);
}

int perf_output_begin_backward(struct perf_output_handle *handle,
                               struct perf_event *event, unsigned int size)
{
        return __perf_output_begin(handle, event, size, true);
}

int perf_output_begin(struct perf_output_handle *handle,
                      struct perf_event *event, unsigned int size)
{

        return __perf_output_begin(handle, event, size,
                                   unlikely(is_write_backward(event)));
}

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);

        /*
         * perf_output_begin() only checks rb->paused, therefore
         * rb->paused must be true if we have no pages for output.
         */
        if (!rb->nr_pages)
                rb->paused = 1;
}

void perf_aux_output_flag(struct perf_output_handle *handle, u64 flags)
{
        /*
         * OVERWRITE is determined by perf_aux_output_end() and can't
         * be passed in directly.
         */
        if (WARN_ON_ONCE(flags & PERF_AUX_FLAG_OVERWRITE))
                return;

        handle->aux_flags |= flags;
}
EXPORT_SYMBOL_GPL(perf_aux_output_flag);

/*
 * This is called before hardware starts writing to the AUX area to
 * obtain an output handle and make sure there's room in the buffer.
 * When the capture completes, call perf_aux_output_end() to commit
 * the recorded data to the buffer.
 *
 * The ordering is similar to that of perf_output_{begin,end}, with
 * the exception of (B), which should be taken care of by the pmu
 * driver, since ordering rules will differ depending on hardware.
 *
 * Call this from pmu::start(); see the comment in perf_aux_output_end()
 * about its use in pmu callbacks. Both can also be called from the PMI
 * handler if needed.
 */
void *perf_aux_output_begin(struct perf_output_handle *handle,
                            struct perf_event *event)
{
        struct perf_event *output_event = event;
        unsigned long aux_head, aux_tail;
        struct ring_buffer *rb;

        if (output_event->parent)
                output_event = output_event->parent;

        /*
         * Since this will typically be open across pmu::add/pmu::del, we
         * grab ring_buffer's refcount instead of holding rcu read lock
         * to make sure it doesn't disappear under us.
         */
        rb = ring_buffer_get(output_event);
        if (!rb)
                return NULL;

        if (!rb_has_aux(rb))
                goto err;

        /*
         * If aux_mmap_count is zero, the aux buffer is in perf_mmap_close(),
         * about to get freed, so we leave immediately.
         *
         * Checking rb::aux_mmap_count and rb::refcount has to be done in
         * the same order, see perf_mmap_close. Otherwise we end up freeing
         * aux pages in this path, which is a bug, because in_atomic().
         */
        if (!atomic_read(&rb->aux_mmap_count))
                goto err;

        if (!atomic_inc_not_zero(&rb->aux_refcount))
                goto err;

        /*
         * Nesting is not supported for AUX area, make sure nested
         * writers are caught early
         */
        if (WARN_ON_ONCE(local_xchg(&rb->aux_nest, 1)))
                goto err_put;

        aux_head = rb->aux_head;

        handle->rb = rb;
        handle->event = event;
        handle->head = aux_head;
        handle->size = 0;
        handle->aux_flags = 0;

        /*
         * In overwrite mode, AUX data stores do not depend on aux_tail,
         * therefore (A) control dependency barrier does not exist. The
         * (B) <-> (C) ordering is still observed by the pmu driver.
         */
        if (!rb->aux_overwrite) {
                aux_tail = READ_ONCE(rb->user_page->aux_tail);
                handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
                if (aux_head - aux_tail < perf_aux_size(rb))
                        handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb));

                /*
                 * handle->size computation depends on aux_tail load; this forms a
                 * control dependency barrier separating aux_tail load from aux data
                 * store that will be enabled on successful return
                 */
                if (!handle->size) { /* A, matches D */
                        event->pending_disable = smp_processor_id();
                        perf_output_wakeup(handle);
                        local_set(&rb->aux_nest, 0);
                        goto err_put;
                }
        }

        return handle->rb->aux_priv;

err_put:
        /* can't be last */
        rb_free_aux(rb);

err:
        ring_buffer_put(rb);
        handle->event = NULL;

        return NULL;
}
EXPORT_SYMBOL_GPL(perf_aux_output_begin);

static __always_inline bool rb_need_aux_wakeup(struct ring_buffer *rb)
{
        if (rb->aux_overwrite)
                return false;

        if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) {
                rb->aux_wakeup = rounddown(rb->aux_head, rb->aux_watermark);
                return true;
        }

        return false;
}

/*
 * Commit the data written by hardware into the ring buffer by adjusting
 * aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the
 * pmu driver's responsibility to observe ordering rules of the hardware,
 * so that all the data is externally visible before this is called.
 *
 * Note: this has to be called from pmu::stop() callback, as the assumption
 * of the AUX buffer management code is that after pmu::stop(), the AUX
 * transaction must be stopped and therefore drop the AUX reference count.
 */
void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
{
        bool wakeup = !!(handle->aux_flags & PERF_AUX_FLAG_TRUNCATED);
        struct ring_buffer *rb = handle->rb;
        unsigned long aux_head;

        /* in overwrite mode, driver provides aux_head via handle */
        if (rb->aux_overwrite) {
                handle->aux_flags |= PERF_AUX_FLAG_OVERWRITE;

                aux_head = handle->head;
                rb->aux_head = aux_head;
        } else {
                handle->aux_flags &= ~PERF_AUX_FLAG_OVERWRITE;

                aux_head = rb->aux_head;
                rb->aux_head += size;
        }

        if (size || handle->aux_flags) {
                /*
                 * Only send RECORD_AUX if we have something useful to communicate
                 */

                perf_event_aux_event(handle->event, aux_head, size,
                                     handle->aux_flags);
        }

        rb->user_page->aux_head = rb->aux_head;
        if (rb_need_aux_wakeup(rb))
                wakeup = true;

        if (wakeup) {
                if (handle->aux_flags & PERF_AUX_FLAG_TRUNCATED)
                        handle->event->pending_disable = smp_processor_id();
                perf_output_wakeup(handle);
        }

        handle->event = NULL;

        local_set(&rb->aux_nest, 0);
        /* can't be last */
        rb_free_aux(rb);
        ring_buffer_put(rb);
}
EXPORT_SYMBOL_GPL(perf_aux_output_end);

/*
 * Skip over a given number of bytes in the AUX buffer, due to, for example,
 * hardware's alignment constraints.
 */
int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)
{
        struct ring_buffer *rb = handle->rb;

        if (size > handle->size)
                return -ENOSPC;

        rb->aux_head += size;

        rb->user_page->aux_head = rb->aux_head;
        if (rb_need_aux_wakeup(rb)) {
                perf_output_wakeup(handle);
                handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
        }

        handle->head = rb->aux_head;
        handle->size -= size;

        return 0;
}
EXPORT_SYMBOL_GPL(perf_aux_output_skip);

void *perf_get_aux(struct perf_output_handle *handle)
{
        /* this is only valid between perf_aux_output_begin and *_end */
        if (!handle->event)
                return NULL;

        return handle->rb->aux_priv;
}
EXPORT_SYMBOL_GPL(perf_get_aux);

#define PERF_AUX_GFP    (GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)

static struct page *rb_alloc_aux_page(int node, int order)
{
        struct page *page;

        if (order > MAX_ORDER)
                order = MAX_ORDER;

        do {
                page = alloc_pages_node(node, PERF_AUX_GFP, order);
        } while (!page && order--);

        if (page && order) {
                /*
                 * Communicate the allocation size to the driver:
                 * if we managed to secure a high-order allocation,
                 * set its first page's private to this order;
                 * !PagePrivate(page) means it's just a normal page.
                 */
                split_page(page, order);
                SetPagePrivate(page);
                set_page_private(page, order);
        }

        return page;
}

static void rb_free_aux_page(struct ring_buffer *rb, int idx)
{
        struct page *page = virt_to_page(rb->aux_pages[idx]);

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

static void __rb_free_aux(struct ring_buffer *rb)
{
        int pg;

        /*
         * Should never happen, the last reference should be dropped from
         * perf_mmap_close() path, which first stops aux transactions (which
         * in turn are the atomic holders of aux_refcount) and then does the
         * last rb_free_aux().
         */
        WARN_ON_ONCE(in_atomic());

        if (rb->aux_priv) {
                rb->free_aux(rb->aux_priv);
                rb->free_aux = NULL;
                rb->aux_priv = NULL;
        }

        if (rb->aux_nr_pages) {
                for (pg = 0; pg < rb->aux_nr_pages; pg++)
                        rb_free_aux_page(rb, pg);

                kfree(rb->aux_pages);
                rb->aux_nr_pages = 0;
        }
}

int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
                 pgoff_t pgoff, int nr_pages, long watermark, int flags)
{
        bool overwrite = !(flags & RING_BUFFER_WRITABLE);
        int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
        int ret = -ENOMEM, max_order = 0;

        if (!has_aux(event))
                return -EOPNOTSUPP;

        if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
                /*
                 * We need to start with the max_order that fits in nr_pages,
                 * not the other way around, hence ilog2() and not get_order.
                 */
                max_order = ilog2(nr_pages);

                /*
                 * PMU requests more than one contiguous chunks of memory
                 * for SW double buffering
                 */
                if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_SW_DOUBLEBUF) &&
                    !overwrite) {
                        if (!max_order)
                                return -EINVAL;

                        max_order--;
                }
        }

        rb->aux_pages = kcalloc_node(nr_pages, sizeof(void *), GFP_KERNEL,
                                     node);
        if (!rb->aux_pages)
                return -ENOMEM;

        rb->free_aux = event->pmu->free_aux;
        for (rb->aux_nr_pages = 0; rb->aux_nr_pages < nr_pages;) {
                struct page *page;
                int last, order;

                order = min(max_order, ilog2(nr_pages - rb->aux_nr_pages));
                page = rb_alloc_aux_page(node, order);
                if (!page)
                        goto out;

                for (last = rb->aux_nr_pages + (1 << page_private(page));
                     last > rb->aux_nr_pages; rb->aux_nr_pages++)
                        rb->aux_pages[rb->aux_nr_pages] = page_address(page++);
        }

        /*
         * In overwrite mode, PMUs that don't support SG may not handle more
         * than one contiguous allocation, since they rely on PMI to do double
         * buffering. In this case, the entire buffer has to be one contiguous
         * chunk.
         */
        if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) &&
            overwrite) {
                struct page *page = virt_to_page(rb->aux_pages[0]);

                if (page_private(page) != max_order)
                        goto out;
        }

        rb->aux_priv = event->pmu->setup_aux(event, rb->aux_pages, nr_pages,
                                             overwrite);
        if (!rb->aux_priv)
                goto out;

        ret = 0;

        /*
         * aux_pages (and pmu driver's private data, aux_priv) will be
         * referenced in both producer's and consumer's contexts, thus
         * we keep a refcount here to make sure either of the two can
         * reference them safely.
         */
        atomic_set(&rb->aux_refcount, 1);

        rb->aux_overwrite = overwrite;
        rb->aux_watermark = watermark;

        if (!rb->aux_watermark && !rb->aux_overwrite)
                rb->aux_watermark = nr_pages << (PAGE_SHIFT - 1);

out:
        if (!ret)
                rb->aux_pgoff = pgoff;
        else
                __rb_free_aux(rb);

        return ret;
}

void rb_free_aux(struct ring_buffer *rb)
{
        if (atomic_dec_and_test(&rb->aux_refcount))
                __rb_free_aux(rb);
}

#ifndef CONFIG_PERF_USE_VMALLOC

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

static 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 *);

        if (order_base_2(size) >= PAGE_SHIFT+MAX_ORDER)
                goto fail;

        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);
}

static 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;
        if (nr_pages) {
                rb->nr_pages = 1;
                rb->page_order = ilog2(nr_pages);
        }

        ring_buffer_init(rb, watermark, flags);

        return rb;

fail_all_buf:
        kfree(rb);

fail:
        return NULL;
}

#endif

struct page *
perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
{
        if (rb->aux_nr_pages) {
                /* above AUX space */
                if (pgoff > rb->aux_pgoff + rb->aux_nr_pages)
                        return NULL;

                /* AUX space */
                if (pgoff >= rb->aux_pgoff) {
                        int aux_pgoff = array_index_nospec(pgoff - rb->aux_pgoff, rb->aux_nr_pages);
                        return virt_to_page(rb->aux_pages[aux_pgoff]);
                }
        }

        return __perf_mmap_to_page(rb, pgoff);
}