// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/memblock.h>
#include <linux/fs.h>
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/memory_hotplug.h>
#include <linux/mm.h>
#include <linux/mmzone.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/page_ext.h>
#include <linux/page_idle.h>

#include "internal.h"

#define BITMAP_CHUNK_SIZE       sizeof(u64)
#define BITMAP_CHUNK_BITS       (BITMAP_CHUNK_SIZE * BITS_PER_BYTE)

/*
 * Idle page tracking only considers user memory pages, for other types of
 * pages the idle flag is always unset and an attempt to set it is silently
 * ignored.
 *
 * We treat a page as a user memory page if it is on an LRU list, because it is
 * always safe to pass such a page to rmap_walk(), which is essential for idle
 * page tracking. With such an indicator of user pages we can skip isolated
 * pages, but since there are not usually many of them, it will hardly affect
 * the overall result.
 *
 * This function tries to get a user memory page by pfn as described above.
 */
static struct folio *page_idle_get_folio(unsigned long pfn)
{
        struct page *page = pfn_to_online_page(pfn);
        struct folio *folio;

        if (!page || PageTail(page))
                return NULL;

        folio = page_folio(page);
        if (!folio_test_lru(folio) || !folio_try_get(folio))
                return NULL;
        if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) {
                folio_put(folio);
                folio = NULL;
        }
        return folio;
}

static bool page_idle_clear_pte_refs_one(struct folio *folio,
                                        struct vm_area_struct *vma,
                                        unsigned long addr, void *arg)
{
        DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, addr, 0);
        bool referenced = false;

        while (page_vma_mapped_walk(&pvmw)) {
                addr = pvmw.address;
                if (pvmw.pte) {
                        /*
                         * For PTE-mapped THP, one sub page is referenced,
                         * the whole THP is referenced.
                         *
                         * PFN swap PTEs, such as device-exclusive ones, that
                         * actually map pages are "old" from a CPU perspective.
                         * The MMU notifier takes care of any device aspects.
                         */
                        if (likely(pte_present(ptep_get(pvmw.pte))))
                                referenced |= ptep_test_and_clear_young(vma, addr, pvmw.pte);
                        referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE);
                } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
                        pmd_t pmdval = pmdp_get(pvmw.pmd);

                        if (likely(pmd_present(pmdval)))
                                referenced |= pmdp_clear_young_notify(vma, addr, pvmw.pmd);
                        referenced |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PMD_SIZE);
                } else {
                        /* unexpected pmd-mapped page? */
                        WARN_ON_ONCE(1);
                }
        }

        if (referenced) {
                folio_clear_idle(folio);
                /*
                 * We cleared the referenced bit in a mapping to this page. To
                 * avoid interference with page reclaim, mark it young so that
                 * folio_referenced() will return > 0.
                 */
                folio_set_young(folio);
        }
        return true;
}

static void page_idle_clear_pte_refs(struct folio *folio)
{
        /*
         * Since rwc.try_lock is unused, rwc is effectively immutable, so we
         * can make it static to save some cycles and stack.
         */
        static struct rmap_walk_control rwc = {
                .rmap_one = page_idle_clear_pte_refs_one,
                .anon_lock = folio_lock_anon_vma_read,
        };

        if (!folio_mapped(folio) || !folio_raw_mapping(folio))
                return;

        if (!folio_trylock(folio))
                return;

        rmap_walk(folio, &rwc);
        folio_unlock(folio);
}

static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
                                     const struct bin_attribute *attr, char *buf,
                                     loff_t pos, size_t count)
{
        u64 *out = (u64 *)buf;
        struct folio *folio;
        unsigned long pfn, end_pfn;
        int bit;

        if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
                return -EINVAL;

        pfn = pos * BITS_PER_BYTE;
        if (pfn >= max_pfn)
                return 0;

        end_pfn = pfn + count * BITS_PER_BYTE;
        if (end_pfn > max_pfn)
                end_pfn = max_pfn;

        for (; pfn < end_pfn; pfn++) {
                bit = pfn % BITMAP_CHUNK_BITS;
                if (!bit)
                        *out = 0ULL;
                folio = page_idle_get_folio(pfn);
                if (folio) {
                        if (folio_test_idle(folio)) {
                                /*
                                 * The page might have been referenced via a
                                 * pte, in which case it is not idle. Clear
                                 * refs and recheck.
                                 */
                                page_idle_clear_pte_refs(folio);
                                if (folio_test_idle(folio))
                                        *out |= 1ULL << bit;
                        }
                        folio_put(folio);
                }
                if (bit == BITMAP_CHUNK_BITS - 1)
                        out++;
                cond_resched();
        }
        return (char *)out - buf;
}

static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
                                      const struct bin_attribute *attr, char *buf,
                                      loff_t pos, size_t count)
{
        const u64 *in = (u64 *)buf;
        struct folio *folio;
        unsigned long pfn, end_pfn;
        int bit;

        if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
                return -EINVAL;

        pfn = pos * BITS_PER_BYTE;
        if (pfn >= max_pfn)
                return -ENXIO;

        end_pfn = pfn + count * BITS_PER_BYTE;
        if (end_pfn > max_pfn)
                end_pfn = max_pfn;

        for (; pfn < end_pfn; pfn++) {
                bit = pfn % BITMAP_CHUNK_BITS;
                if ((*in >> bit) & 1) {
                        folio = page_idle_get_folio(pfn);
                        if (folio) {
                                page_idle_clear_pte_refs(folio);
                                folio_set_idle(folio);
                                folio_put(folio);
                        }
                }
                if (bit == BITMAP_CHUNK_BITS - 1)
                        in++;
                cond_resched();
        }
        return (char *)in - buf;
}

static const struct bin_attribute page_idle_bitmap_attr =
                __BIN_ATTR(bitmap, 0600,
                           page_idle_bitmap_read, page_idle_bitmap_write, 0);

static const struct bin_attribute *const page_idle_bin_attrs[] = {
        &page_idle_bitmap_attr,
        NULL,
};

static const struct attribute_group page_idle_attr_group = {
        .bin_attrs = page_idle_bin_attrs,
        .name = "page_idle",
};

static int __init page_idle_init(void)
{
        int err;

        err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
        if (err) {
                pr_err("page_idle: register sysfs failed\n");
                return err;
        }
        return 0;
}
subsys_initcall(page_idle_init);