Merge tag 'hardening-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-stable.git] / mm / page_isolation.c

// 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>

/*
 * This function checks whether the range [start_pfn, end_pfn) includes
 * unmovable pages or not. The range must fall into a single pageblock and
 * consequently belong to a single zone.
 *
 * PageLRU check without isolation or lru_lock could race so that
 * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable
 * check without lock_page also may miss some movable non-lru pages at
 * race condition. So you can't expect this function should be exact.
 *
 * Returns a page without holding a reference. If the caller wants to
 * dereference that page (e.g., dumping), it has to make sure that it
 * cannot get removed (e.g., via memory unplug) concurrently.
 *
 */
static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long end_pfn,
                                int migratetype, int flags)
{
        struct page *page = pfn_to_page(start_pfn);
        struct zone *zone = page_zone(page);
        unsigned long pfn;

        VM_BUG_ON(pageblock_start_pfn(start_pfn) !=
                  pageblock_start_pfn(end_pfn - 1));

        if (is_migrate_cma_page(page)) {
                /*
                 * CMA allocations (alloc_contig_range) really need to mark
                 * isolate CMA pageblocks even when they are not movable in fact
                 * so consider them movable here.
                 */
                if (is_migrate_cma(migratetype))
                        return NULL;

                return page;
        }

        for (pfn = start_pfn; pfn < end_pfn; pfn++) {
                page = pfn_to_page(pfn);

                /*
                 * Both, bootmem allocations and memory holes are marked
                 * PG_reserved and are unmovable. We can even have unmovable
                 * allocations inside ZONE_MOVABLE, for example when
                 * specifying "movablecore".
                 */
                if (PageReserved(page))
                        return page;

                /*
                 * If the zone is movable and we have ruled out all reserved
                 * pages then it should be reasonably safe to assume the rest
                 * is movable.
                 */
                if (zone_idx(zone) == ZONE_MOVABLE)
                        continue;

                /*
                 * Hugepages are not in LRU lists, but they're movable.
                 * THPs are on the LRU, but need to be counted as #small pages.
                 * We need not scan over tail pages because we don't
                 * handle each tail page individually in migration.
                 */
                if (PageHuge(page) || PageTransCompound(page)) {
                        struct folio *folio = page_folio(page);
                        unsigned int skip_pages;

                        if (PageHuge(page)) {
                                if (!hugepage_migration_supported(folio_hstate(folio)))
                                        return page;
                        } else if (!folio_test_lru(folio) && !__folio_test_movable(folio)) {
                                return page;
                        }

                        skip_pages = folio_nr_pages(folio) - folio_page_idx(folio, page);
                        pfn += skip_pages - 1;
                        continue;
                }

                /*
                 * We can't use page_count without pin a page
                 * because another CPU can free compound page.
                 * This check already skips compound tails of THP
                 * because their page->_refcount is zero at all time.
                 */
                if (!page_ref_count(page)) {
                        if (PageBuddy(page))
                                pfn += (1 << buddy_order(page)) - 1;
                        continue;
                }

                /*
                 * The HWPoisoned page may be not in buddy system, and
                 * page_count() is not 0.
                 */
                if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
                        continue;

                /*
                 * We treat all PageOffline() pages as movable when offlining
                 * to give drivers a chance to decrement their reference count
                 * in MEM_GOING_OFFLINE in order to indicate that these pages
                 * can be offlined as there are no direct references anymore.
                 * For actually unmovable PageOffline() where the driver does
                 * not support this, we will fail later when trying to actually
                 * move these pages that still have a reference count > 0.
                 * (false negatives in this function only)
                 */
                if ((flags & MEMORY_OFFLINE) && PageOffline(page))
                        continue;

                if (__PageMovable(page) || PageLRU(page))
                        continue;

                /*
                 * If there are RECLAIMABLE pages, we need to check
                 * it.  But now, memory offline itself doesn't call
                 * shrink_node_slabs() and it still to be fixed.
                 */
                return page;
        }
        return NULL;
}

/*
 * This function set pageblock migratetype to isolate if no unmovable page is
 * present in [start_pfn, end_pfn). The pageblock must intersect with
 * [start_pfn, end_pfn).
 */
static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags,
                        unsigned long start_pfn, unsigned long end_pfn)
{
        struct zone *zone = page_zone(page);
        struct page *unmovable;
        unsigned long flags;
        unsigned long check_unmovable_start, check_unmovable_end;

        if (PageUnaccepted(page))
                accept_page(page);

        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.
         *
         * Pass the intersection of [start_pfn, end_pfn) and the page's pageblock
         * to avoid redundant checks.
         */
        check_unmovable_start = max(page_to_pfn(page), start_pfn);
        check_unmovable_end = min(pageblock_end_pfn(page_to_pfn(page)),
                                  end_pfn);

        unmovable = has_unmovable_pages(check_unmovable_start, check_unmovable_end,
                        migratetype, isol_flags);
        if (!unmovable) {
                if (!move_freepages_block_isolate(zone, page, MIGRATE_ISOLATE)) {
                        spin_unlock_irqrestore(&zone->lock, flags);
                        return -EBUSY;
                }
                zone->nr_isolate_pageblock++;
                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, int migratetype)
{
        struct zone *zone;
        unsigned long flags;
        bool isolated_page = false;
        unsigned int order;
        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_PAGE_ORDER) {
                        buddy = find_buddy_page_pfn(page, page_to_pfn(page),
                                                    order, NULL);
                        if (buddy && !is_migrate_isolate_page(buddy)) {
                                isolated_page = !!__isolate_free_page(page, order);
                                /*
                                 * Isolating a free page in an isolated pageblock
                                 * is expected to always work as watermarks don't
                                 * apply here.
                                 */
                                VM_WARN_ON(!isolated_page);
                        }
                }
        }

        /*
         * 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) {
                /*
                 * Isolating this block already succeeded, so this
                 * should not fail on zone boundaries.
                 */
                WARN_ON_ONCE(!move_freepages_block_isolate(zone, page, migratetype));
        } else {
                set_pageblock_migratetype(page, migratetype);
                __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;
}

/**
 * isolate_single_pageblock() -- tries to isolate a pageblock that might be
 * within a free or in-use page.
 * @boundary_pfn:               pageblock-aligned pfn that a page might cross
 * @flags:                      isolation flags
 * @isolate_before:     isolate the pageblock before the boundary_pfn
 * @skip_isolation:     the flag to skip the pageblock isolation in second
 *                      isolate_single_pageblock()
 * @migratetype:        migrate type to set in error recovery.
 *
 * Free and in-use pages can be as big as MAX_PAGE_ORDER and contain more than one
 * pageblock. When not all pageblocks within a page are isolated at the same
 * time, free page accounting can go wrong. For example, in the case of
 * MAX_PAGE_ORDER = pageblock_order + 1, a MAX_PAGE_ORDER page has two
 * pagelbocks.
 * [      MAX_PAGE_ORDER         ]
 * [  pageblock0  |  pageblock1  ]
 * When either pageblock is isolated, if it is a free page, the page is not
 * split into separate migratetype lists, which is supposed to; if it is an
 * in-use page and freed later, __free_one_page() does not split the free page
 * either. The function handles this by splitting the free page or migrating
 * the in-use page then splitting the free page.
 */
static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
                bool isolate_before, bool skip_isolation, int migratetype)
{
        unsigned long start_pfn;
        unsigned long isolate_pageblock;
        unsigned long pfn;
        struct zone *zone;
        int ret;

        VM_BUG_ON(!pageblock_aligned(boundary_pfn));

        if (isolate_before)
                isolate_pageblock = boundary_pfn - pageblock_nr_pages;
        else
                isolate_pageblock = boundary_pfn;

        /*
         * scan at the beginning of MAX_ORDER_NR_PAGES aligned range to avoid
         * only isolating a subset of pageblocks from a bigger than pageblock
         * free or in-use page. Also make sure all to-be-isolated pageblocks
         * are within the same zone.
         */
        zone  = page_zone(pfn_to_page(isolate_pageblock));
        start_pfn  = max(ALIGN_DOWN(isolate_pageblock, MAX_ORDER_NR_PAGES),
                                      zone->zone_start_pfn);

        if (skip_isolation) {
                int mt __maybe_unused = get_pageblock_migratetype(pfn_to_page(isolate_pageblock));

                VM_BUG_ON(!is_migrate_isolate(mt));
        } else {
                ret = set_migratetype_isolate(pfn_to_page(isolate_pageblock), migratetype,
                                flags, isolate_pageblock, isolate_pageblock + pageblock_nr_pages);

                if (ret)
                        return ret;
        }

        /*
         * Bail out early when the to-be-isolated pageblock does not form
         * a free or in-use page across boundary_pfn:
         *
         * 1. isolate before boundary_pfn: the page after is not online
         * 2. isolate after boundary_pfn: the page before is not online
         *
         * This also ensures correctness. Without it, when isolate after
         * boundary_pfn and [start_pfn, boundary_pfn) are not online,
         * __first_valid_page() will return unexpected NULL in the for loop
         * below.
         */
        if (isolate_before) {
                if (!pfn_to_online_page(boundary_pfn))
                        return 0;
        } else {
                if (!pfn_to_online_page(boundary_pfn - 1))
                        return 0;
        }

        for (pfn = start_pfn; pfn < boundary_pfn;) {
                struct page *page = __first_valid_page(pfn, boundary_pfn - pfn);

                VM_BUG_ON(!page);
                pfn = page_to_pfn(page);

                if (PageUnaccepted(page)) {
                        pfn += MAX_ORDER_NR_PAGES;
                        continue;
                }

                if (PageBuddy(page)) {
                        int order = buddy_order(page);

                        /* move_freepages_block_isolate() handled this */
                        VM_WARN_ON_ONCE(pfn + (1 << order) > boundary_pfn);

                        pfn += 1UL << order;
                        continue;
                }

                /*
                 * If a compound page is straddling our block, attempt
                 * to migrate it out of the way.
                 *
                 * We don't have to worry about this creating a large
                 * free page that straddles into our block: gigantic
                 * pages are freed as order-0 chunks, and LRU pages
                 * (currently) do not exceed pageblock_order.
                 *
                 * The block of interest has already been marked
                 * MIGRATE_ISOLATE above, so when migration is done it
                 * will free its pages onto the correct freelists.
                 */
                if (PageCompound(page)) {
                        struct page *head = compound_head(page);
                        unsigned long head_pfn = page_to_pfn(head);
                        unsigned long nr_pages = compound_nr(head);

                        if (head_pfn + nr_pages <= boundary_pfn ||
                            PageHuge(page)) {
                                pfn = head_pfn + nr_pages;
                                continue;
                        }

                        /*
                         * These pages are movable too, but they're
                         * not expected to exceed pageblock_order.
                         *
                         * Let us know when they do, so we can add
                         * proper free and split handling for them.
                         */
                        VM_WARN_ON_ONCE_PAGE(PageLRU(page), page);
                        VM_WARN_ON_ONCE_PAGE(__PageMovable(page), page);

                        goto failed;
                }

                pfn++;
        }
        return 0;
failed:
        /* restore the original migratetype */
        if (!skip_isolation)
                unset_migratetype_isolate(pfn_to_page(isolate_pageblock), migratetype);
        return -EBUSY;
}

/**
 * start_isolate_page_range() - mark page range MIGRATE_ISOLATE
 * @start_pfn:          The first PFN of the range to be isolated.
 * @end_pfn:            The last PFN of the range to be isolated.
 * @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.
 *
 * The function first tries to isolate the pageblocks at the beginning and end
 * of the range, since there might be pages across the range boundaries.
 * Afterwards, it isolates the rest of the range.
 *
 * 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,
                             int migratetype, int flags)
{
        unsigned long pfn;
        struct page *page;
        /* isolation is done at page block granularity */
        unsigned long isolate_start = pageblock_start_pfn(start_pfn);
        unsigned long isolate_end = pageblock_align(end_pfn);
        int ret;
        bool skip_isolation = false;

        /* isolate [isolate_start, isolate_start + pageblock_nr_pages) pageblock */
        ret = isolate_single_pageblock(isolate_start, flags, false,
                        skip_isolation, migratetype);
        if (ret)
                return ret;

        if (isolate_start == isolate_end - pageblock_nr_pages)
                skip_isolation = true;

        /* isolate [isolate_end - pageblock_nr_pages, isolate_end) pageblock */
        ret = isolate_single_pageblock(isolate_end, flags, true,
                        skip_isolation, migratetype);
        if (ret) {
                unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
                return ret;
        }

        /* skip isolated pageblocks at the beginning and end */
        for (pfn = isolate_start + pageblock_nr_pages;
             pfn < isolate_end - pageblock_nr_pages;
             pfn += pageblock_nr_pages) {
                page = __first_valid_page(pfn, pageblock_nr_pages);
                if (page && set_migratetype_isolate(page, migratetype, flags,
                                        start_pfn, end_pfn)) {
                        undo_isolate_page_range(isolate_start, pfn, migratetype);
                        unset_migratetype_isolate(
                                pfn_to_page(isolate_end - pageblock_nr_pages),
                                migratetype);
                        return -EBUSY;
                }
        }
        return 0;
}

/**
 * undo_isolate_page_range - undo effects of start_isolate_page_range()
 * @start_pfn:          The first PFN of the isolated range
 * @end_pfn:            The last PFN of the isolated range
 * @migratetype:        New migrate type to set on the range
 *
 * This finds every MIGRATE_ISOLATE page block in the given range
 * and switches it to @migratetype.
 */
void undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
                            int migratetype)
{
        unsigned long pfn;
        struct page *page;
        unsigned long isolate_start = pageblock_start_pfn(start_pfn);
        unsigned long isolate_end = pageblock_align(end_pfn);

        for (pfn = isolate_start;
             pfn < isolate_end;
             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) {
                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;
}

/**
 * test_pages_isolated - check if pageblocks in range are isolated
 * @start_pfn:          The first PFN of the isolated range
 * @end_pfn:            The first PFN *after* the isolated range
 * @isol_flags:         Testing mode flags
 *
 * This tests if all in the specified range are free.
 *
 * If %MEMORY_OFFLINE is specified in @flags, it will consider
 * poisoned and offlined pages free as well.
 *
 * Caller must ensure the requested range doesn't span zones.
 *
 * Returns 0 if true, -EBUSY if one or more pages are in use.
 */
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;
        int ret;

        /*
         * Note: pageblock_nr_pages != MAX_PAGE_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) {
                ret = -EBUSY;
                goto out;
        }

        /* 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);

        ret = pfn < end_pfn ? -EBUSY : 0;

out:
        trace_test_pages_isolated(start_pfn, end_pfn, pfn);

        return ret;
}