// SPDX-License-Identifier: GPL-2.0
/*
 * linux/mm/page_isolation.c
 */

#include <linux/mm.h>
#include <linux/page-isolation.h>
#include <linux/pageblock-flags.h>
#include <linux/memory.h>
#include <linux/hugetlb.h>
#include <linux/page_owner.h>
#include <linux/migrate.h>
#include "internal.h"

#define CREATE_TRACE_POINTS
#include <trace/events/page_isolation.h>

static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags)
{
        struct zone *zone = page_zone(page);
        struct page *unmovable;
        unsigned long flags;

        spin_lock_irqsave(&zone->lock, flags);

        /*
         * We assume the caller intended to SET migrate type to isolate.
         * If it is already set, then someone else must have raced and
         * set it before us.
         */
        if (is_migrate_isolate_page(page)) {
                spin_unlock_irqrestore(&zone->lock, flags);
                return -EBUSY;
        }

        /*
         * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
         * We just check MOVABLE pages.
         */
        unmovable = has_unmovable_pages(zone, page, migratetype, isol_flags);
        if (!unmovable) {
                unsigned long nr_pages;
                int mt = get_pageblock_migratetype(page);

                set_pageblock_migratetype(page, MIGRATE_ISOLATE);
                zone->nr_isolate_pageblock++;
                nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
                                                                        NULL);

                __mod_zone_freepage_state(zone, -nr_pages, mt);
                spin_unlock_irqrestore(&zone->lock, flags);
                return 0;
        }

        spin_unlock_irqrestore(&zone->lock, flags);
        if (isol_flags & REPORT_FAILURE) {
                /*
                 * printk() with zone->lock held will likely trigger a
                 * lockdep splat, so defer it here.
                 */
                dump_page(unmovable, "unmovable page");
        }

        return -EBUSY;
}

static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
{
        struct zone *zone;
        unsigned long flags, nr_pages;
        bool isolated_page = false;
        unsigned int order;
        unsigned long pfn, buddy_pfn;
        struct page *buddy;

        zone = page_zone(page);
        spin_lock_irqsave(&zone->lock, flags);
        if (!is_migrate_isolate_page(page))
                goto out;

        /*
         * Because freepage with more than pageblock_order on isolated
         * pageblock is restricted to merge due to freepage counting problem,
         * it is possible that there is free buddy page.
         * move_freepages_block() doesn't care of merge so we need other
         * approach in order to merge them. Isolation and free will make
         * these pages to be merged.
         */
        if (PageBuddy(page)) {
                order = buddy_order(page);
                if (order >= pageblock_order && order < MAX_ORDER - 1) {
                        pfn = page_to_pfn(page);
                        buddy_pfn = __find_buddy_pfn(pfn, order);
                        buddy = page + (buddy_pfn - pfn);

                        if (pfn_valid_within(buddy_pfn) &&
                            !is_migrate_isolate_page(buddy)) {
                                __isolate_free_page(page, order);
                                isolated_page = true;
                        }
                }
        }

        /*
         * If we isolate freepage with more than pageblock_order, there
         * should be no freepage in the range, so we could avoid costly
         * pageblock scanning for freepage moving.
         *
         * We didn't actually touch any of the isolated pages, so place them
         * to the tail of the freelist. This is an optimization for memory
         * onlining - just onlined memory won't immediately be considered for
         * allocation.
         */
        if (!isolated_page) {
                nr_pages = move_freepages_block(zone, page, migratetype, NULL);
                __mod_zone_freepage_state(zone, nr_pages, migratetype);
        }
        set_pageblock_migratetype(page, migratetype);
        if (isolated_page)
                __putback_isolated_page(page, order, migratetype);
        zone->nr_isolate_pageblock--;
out:
        spin_unlock_irqrestore(&zone->lock, flags);
}

static inline struct page *
__first_valid_page(unsigned long pfn, unsigned long nr_pages)
{
        int i;

        for (i = 0; i < nr_pages; i++) {
                struct page *page;

                page = pfn_to_online_page(pfn + i);
                if (!page)
                        continue;
                return page;
        }
        return NULL;
}

/**
 * start_isolate_page_range() - make page-allocation-type of range of pages to
 * be MIGRATE_ISOLATE.
 * @start_pfn:          The lower PFN of the range to be isolated.
 * @end_pfn:            The upper PFN of the range to be isolated.
 *                      start_pfn/end_pfn must be aligned to pageblock_order.
 * @migratetype:        Migrate type to set in error recovery.
 * @flags:              The following flags are allowed (they can be combined in
 *                      a bit mask)
 *                      MEMORY_OFFLINE - isolate to offline (!allocate) memory
 *                                       e.g., skip over PageHWPoison() pages
 *                                       and PageOffline() pages.
 *                      REPORT_FAILURE - report details about the failure to
 *                      isolate the range
 *
 * Making page-allocation-type to be MIGRATE_ISOLATE means free pages in
 * the range will never be allocated. Any free pages and pages freed in the
 * future will not be allocated again. If specified range includes migrate types
 * other than MOVABLE or CMA, this will fail with -EBUSY. For isolating all
 * pages in the range finally, the caller have to free all pages in the range.
 * test_page_isolated() can be used for test it.
 *
 * There is no high level synchronization mechanism that prevents two threads
 * from trying to isolate overlapping ranges. If this happens, one thread
 * will notice pageblocks in the overlapping range already set to isolate.
 * This happens in set_migratetype_isolate, and set_migratetype_isolate
 * returns an error. We then clean up by restoring the migration type on
 * pageblocks we may have modified and return -EBUSY to caller. This
 * prevents two threads from simultaneously working on overlapping ranges.
 *
 * Please note that there is no strong synchronization with the page allocator
 * either. Pages might be freed while their page blocks are marked ISOLATED.
 * A call to drain_all_pages() after isolation can flush most of them. However
 * in some cases pages might still end up on pcp lists and that would allow
 * for their allocation even when they are in fact isolated already. Depending
 * on how strong of a guarantee the caller needs, zone_pcp_disable/enable()
 * might be used to flush and disable pcplist before isolation and enable after
 * unisolation.
 *
 * Return: 0 on success and -EBUSY if any part of range cannot be isolated.
 */
int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
                             unsigned migratetype, int flags)
{
        unsigned long pfn;
        unsigned long undo_pfn;
        struct page *page;

        BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
        BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));

        for (pfn = start_pfn;
             pfn < end_pfn;
             pfn += pageblock_nr_pages) {
                page = __first_valid_page(pfn, pageblock_nr_pages);
                if (page) {
                        if (set_migratetype_isolate(page, migratetype, flags)) {
                                undo_pfn = pfn;
                                goto undo;
                        }
                }
        }
        return 0;
undo:
        for (pfn = start_pfn;
             pfn < undo_pfn;
             pfn += pageblock_nr_pages) {
                struct page *page = pfn_to_online_page(pfn);
                if (!page)
                        continue;
                unset_migratetype_isolate(page, migratetype);
        }

        return -EBUSY;
}

/*
 * Make isolated pages available again.
 */
void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
                            unsigned migratetype)
{
        unsigned long pfn;
        struct page *page;

        BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
        BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));

        for (pfn = start_pfn;
             pfn < end_pfn;
             pfn += pageblock_nr_pages) {
                page = __first_valid_page(pfn, pageblock_nr_pages);
                if (!page || !is_migrate_isolate_page(page))
                        continue;
                unset_migratetype_isolate(page, migratetype);
        }
}
/*
 * Test all pages in the range is free(means isolated) or not.
 * all pages in [start_pfn...end_pfn) must be in the same zone.
 * zone->lock must be held before call this.
 *
 * Returns the last tested pfn.
 */
static unsigned long
__test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
                                  int flags)
{
        struct page *page;

        while (pfn < end_pfn) {
                if (!pfn_valid_within(pfn)) {
                        pfn++;
                        continue;
                }
                page = pfn_to_page(pfn);
                if (PageBuddy(page))
                        /*
                         * If the page is on a free list, it has to be on
                         * the correct MIGRATE_ISOLATE freelist. There is no
                         * simple way to verify that as VM_BUG_ON(), though.
                         */
                        pfn += 1 << buddy_order(page);
                else if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
                        /* A HWPoisoned page cannot be also PageBuddy */
                        pfn++;
                else if ((flags & MEMORY_OFFLINE) && PageOffline(page) &&
                         !page_count(page))
                        /*
                         * The responsible driver agreed to skip PageOffline()
                         * pages when offlining memory by dropping its
                         * reference in MEM_GOING_OFFLINE.
                         */
                        pfn++;
                else
                        break;
        }

        return pfn;
}

/* Caller should ensure that requested range is in a single zone */
int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn,
                        int isol_flags)
{
        unsigned long pfn, flags;
        struct page *page;
        struct zone *zone;

        /*
         * Note: pageblock_nr_pages != MAX_ORDER. Then, chunks of free pages
         * are not aligned to pageblock_nr_pages.
         * Then we just check migratetype first.
         */
        for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
                page = __first_valid_page(pfn, pageblock_nr_pages);
                if (page && !is_migrate_isolate_page(page))
                        break;
        }
        page = __first_valid_page(start_pfn, end_pfn - start_pfn);
        if ((pfn < end_pfn) || !page)
                return -EBUSY;
        /* Check all pages are free or marked as ISOLATED */
        zone = page_zone(page);
        spin_lock_irqsave(&zone->lock, flags);
        pfn = __test_page_isolated_in_pageblock(start_pfn, end_pfn, isol_flags);
        spin_unlock_irqrestore(&zone->lock, flags);

        trace_test_pages_isolated(start_pfn, end_pfn, pfn);

        return pfn < end_pfn ? -EBUSY : 0;
}