// SPDX-License-Identifier: GPL-2.0
/*
 * High memory handling common code and variables.
 *
 * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
 *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
 *
 *
 * Redesigned the x86 32-bit VM architecture to deal with
 * 64-bit physical space. With current x86 CPUs this
 * means up to 64 Gigabytes physical RAM.
 *
 * Rewrote high memory support to move the page cache into
 * high memory. Implemented permanent (schedulable) kmaps
 * based on Linus' idea.
 *
 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
 */

#include <linux/mm.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/pagemap.h>
#include <linux/mempool.h>
#include <linux/blkdev.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/highmem.h>
#include <linux/kgdb.h>
#include <asm/tlbflush.h>


#if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
DEFINE_PER_CPU(int, __kmap_atomic_idx);
#endif

/*
 * Virtual_count is not a pure "count".
 *  0 means that it is not mapped, and has not been mapped
 *    since a TLB flush - it is usable.
 *  1 means that there are no users, but it has been mapped
 *    since the last TLB flush - so we can't use it.
 *  n means that there are (n-1) current users of it.
 */
#ifdef CONFIG_HIGHMEM

/*
 * Architecture with aliasing data cache may define the following family of
 * helper functions in its asm/highmem.h to control cache color of virtual
 * addresses where physical memory pages are mapped by kmap.
 */
#ifndef get_pkmap_color

/*
 * Determine color of virtual address where the page should be mapped.
 */
static inline unsigned int get_pkmap_color(struct page *page)
{
        return 0;
}
#define get_pkmap_color get_pkmap_color

/*
 * Get next index for mapping inside PKMAP region for page with given color.
 */
static inline unsigned int get_next_pkmap_nr(unsigned int color)
{
        static unsigned int last_pkmap_nr;

        last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
        return last_pkmap_nr;
}

/*
 * Determine if page index inside PKMAP region (pkmap_nr) of given color
 * has wrapped around PKMAP region end. When this happens an attempt to
 * flush all unused PKMAP slots is made.
 */
static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
{
        return pkmap_nr == 0;
}

/*
 * Get the number of PKMAP entries of the given color. If no free slot is
 * found after checking that many entries, kmap will sleep waiting for
 * someone to call kunmap and free PKMAP slot.
 */
static inline int get_pkmap_entries_count(unsigned int color)
{
        return LAST_PKMAP;
}

/*
 * Get head of a wait queue for PKMAP entries of the given color.
 * Wait queues for different mapping colors should be independent to avoid
 * unnecessary wakeups caused by freeing of slots of other colors.
 */
static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
{
        static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);

        return &pkmap_map_wait;
}
#endif

atomic_long_t _totalhigh_pages __read_mostly;
EXPORT_SYMBOL(_totalhigh_pages);

EXPORT_PER_CPU_SYMBOL(__kmap_atomic_idx);

unsigned int nr_free_highpages (void)
{
        struct zone *zone;
        unsigned int pages = 0;

        for_each_populated_zone(zone) {
                if (is_highmem(zone))
                        pages += zone_page_state(zone, NR_FREE_PAGES);
        }

        return pages;
}

static int pkmap_count[LAST_PKMAP];
static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);

pte_t * pkmap_page_table;

/*
 * Most architectures have no use for kmap_high_get(), so let's abstract
 * the disabling of IRQ out of the locking in that case to save on a
 * potential useless overhead.
 */
#ifdef ARCH_NEEDS_KMAP_HIGH_GET
#define lock_kmap()             spin_lock_irq(&kmap_lock)
#define unlock_kmap()           spin_unlock_irq(&kmap_lock)
#define lock_kmap_any(flags)    spin_lock_irqsave(&kmap_lock, flags)
#define unlock_kmap_any(flags)  spin_unlock_irqrestore(&kmap_lock, flags)
#else
#define lock_kmap()             spin_lock(&kmap_lock)
#define unlock_kmap()           spin_unlock(&kmap_lock)
#define lock_kmap_any(flags)    \
                do { spin_lock(&kmap_lock); (void)(flags); } while (0)
#define unlock_kmap_any(flags)  \
                do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
#endif

struct page *kmap_to_page(void *vaddr)
{
        unsigned long addr = (unsigned long)vaddr;

        if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) {
                int i = PKMAP_NR(addr);
                return pte_page(pkmap_page_table[i]);
        }

        return virt_to_page(addr);
}
EXPORT_SYMBOL(kmap_to_page);

static void flush_all_zero_pkmaps(void)
{
        int i;
        int need_flush = 0;

        flush_cache_kmaps();

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

                /*
                 * zero means we don't have anything to do,
                 * >1 means that it is still in use. Only
                 * a count of 1 means that it is free but
                 * needs to be unmapped
                 */
                if (pkmap_count[i] != 1)
                        continue;
                pkmap_count[i] = 0;

                /* sanity check */
                BUG_ON(pte_none(pkmap_page_table[i]));

                /*
                 * Don't need an atomic fetch-and-clear op here;
                 * no-one has the page mapped, and cannot get at
                 * its virtual address (and hence PTE) without first
                 * getting the kmap_lock (which is held here).
                 * So no dangers, even with speculative execution.
                 */
                page = pte_page(pkmap_page_table[i]);
                pte_clear(&init_mm, PKMAP_ADDR(i), &pkmap_page_table[i]);

                set_page_address(page, NULL);
                need_flush = 1;
        }
        if (need_flush)
                flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
}

/**
 * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
 */
void kmap_flush_unused(void)
{
        lock_kmap();
        flush_all_zero_pkmaps();
        unlock_kmap();
}

static inline unsigned long map_new_virtual(struct page *page)
{
        unsigned long vaddr;
        int count;
        unsigned int last_pkmap_nr;
        unsigned int color = get_pkmap_color(page);

start:
        count = get_pkmap_entries_count(color);
        /* Find an empty entry */
        for (;;) {
                last_pkmap_nr = get_next_pkmap_nr(color);
                if (no_more_pkmaps(last_pkmap_nr, color)) {
                        flush_all_zero_pkmaps();
                        count = get_pkmap_entries_count(color);
                }
                if (!pkmap_count[last_pkmap_nr])
                        break;  /* Found a usable entry */
                if (--count)
                        continue;

                /*
                 * Sleep for somebody else to unmap their entries
                 */
                {
                        DECLARE_WAITQUEUE(wait, current);
                        wait_queue_head_t *pkmap_map_wait =
                                get_pkmap_wait_queue_head(color);

                        __set_current_state(TASK_UNINTERRUPTIBLE);
                        add_wait_queue(pkmap_map_wait, &wait);
                        unlock_kmap();
                        schedule();
                        remove_wait_queue(pkmap_map_wait, &wait);
                        lock_kmap();

                        /* Somebody else might have mapped it while we slept */
                        if (page_address(page))
                                return (unsigned long)page_address(page);

                        /* Re-start */
                        goto start;
                }
        }
        vaddr = PKMAP_ADDR(last_pkmap_nr);
        set_pte_at(&init_mm, vaddr,
                   &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));

        pkmap_count[last_pkmap_nr] = 1;
        set_page_address(page, (void *)vaddr);

        return vaddr;
}

/**
 * kmap_high - map a highmem page into memory
 * @page: &struct page to map
 *
 * Returns the page's virtual memory address.
 *
 * We cannot call this from interrupts, as it may block.
 */
void *kmap_high(struct page *page)
{
        unsigned long vaddr;

        /*
         * For highmem pages, we can't trust "virtual" until
         * after we have the lock.
         */
        lock_kmap();
        vaddr = (unsigned long)page_address(page);
        if (!vaddr)
                vaddr = map_new_virtual(page);
        pkmap_count[PKMAP_NR(vaddr)]++;
        BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
        unlock_kmap();
        return (void*) vaddr;
}

EXPORT_SYMBOL(kmap_high);

#ifdef ARCH_NEEDS_KMAP_HIGH_GET
/**
 * kmap_high_get - pin a highmem page into memory
 * @page: &struct page to pin
 *
 * Returns the page's current virtual memory address, or NULL if no mapping
 * exists.  If and only if a non null address is returned then a
 * matching call to kunmap_high() is necessary.
 *
 * This can be called from any context.
 */
void *kmap_high_get(struct page *page)
{
        unsigned long vaddr, flags;

        lock_kmap_any(flags);
        vaddr = (unsigned long)page_address(page);
        if (vaddr) {
                BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
                pkmap_count[PKMAP_NR(vaddr)]++;
        }
        unlock_kmap_any(flags);
        return (void*) vaddr;
}
#endif

/**
 * kunmap_high - unmap a highmem page into memory
 * @page: &struct page to unmap
 *
 * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
 * only from user context.
 */
void kunmap_high(struct page *page)
{
        unsigned long vaddr;
        unsigned long nr;
        unsigned long flags;
        int need_wakeup;
        unsigned int color = get_pkmap_color(page);
        wait_queue_head_t *pkmap_map_wait;

        lock_kmap_any(flags);
        vaddr = (unsigned long)page_address(page);
        BUG_ON(!vaddr);
        nr = PKMAP_NR(vaddr);

        /*
         * A count must never go down to zero
         * without a TLB flush!
         */
        need_wakeup = 0;
        switch (--pkmap_count[nr]) {
        case 0:
                BUG();
        case 1:
                /*
                 * Avoid an unnecessary wake_up() function call.
                 * The common case is pkmap_count[] == 1, but
                 * no waiters.
                 * The tasks queued in the wait-queue are guarded
                 * by both the lock in the wait-queue-head and by
                 * the kmap_lock.  As the kmap_lock is held here,
                 * no need for the wait-queue-head's lock.  Simply
                 * test if the queue is empty.
                 */
                pkmap_map_wait = get_pkmap_wait_queue_head(color);
                need_wakeup = waitqueue_active(pkmap_map_wait);
        }
        unlock_kmap_any(flags);

        /* do wake-up, if needed, race-free outside of the spin lock */
        if (need_wakeup)
                wake_up(pkmap_map_wait);
}

EXPORT_SYMBOL(kunmap_high);
#endif

#if defined(HASHED_PAGE_VIRTUAL)

#define PA_HASH_ORDER   7

/*
 * Describes one page->virtual association
 */
struct page_address_map {
        struct page *page;
        void *virtual;
        struct list_head list;
};

static struct page_address_map page_address_maps[LAST_PKMAP];

/*
 * Hash table bucket
 */
static struct page_address_slot {
        struct list_head lh;                    /* List of page_address_maps */
        spinlock_t lock;                        /* Protect this bucket's list */
} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];

static struct page_address_slot *page_slot(const struct page *page)
{
        return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
}

/**
 * page_address - get the mapped virtual address of a page
 * @page: &struct page to get the virtual address of
 *
 * Returns the page's virtual address.
 */
void *page_address(const struct page *page)
{
        unsigned long flags;
        void *ret;
        struct page_address_slot *pas;

        if (!PageHighMem(page))
                return lowmem_page_address(page);

        pas = page_slot(page);
        ret = NULL;
        spin_lock_irqsave(&pas->lock, flags);
        if (!list_empty(&pas->lh)) {
                struct page_address_map *pam;

                list_for_each_entry(pam, &pas->lh, list) {
                        if (pam->page == page) {
                                ret = pam->virtual;
                                goto done;
                        }
                }
        }
done:
        spin_unlock_irqrestore(&pas->lock, flags);
        return ret;
}

EXPORT_SYMBOL(page_address);

/**
 * set_page_address - set a page's virtual address
 * @page: &struct page to set
 * @virtual: virtual address to use
 */
void set_page_address(struct page *page, void *virtual)
{
        unsigned long flags;
        struct page_address_slot *pas;
        struct page_address_map *pam;

        BUG_ON(!PageHighMem(page));

        pas = page_slot(page);
        if (virtual) {          /* Add */
                pam = &page_address_maps[PKMAP_NR((unsigned long)virtual)];
                pam->page = page;
                pam->virtual = virtual;

                spin_lock_irqsave(&pas->lock, flags);
                list_add_tail(&pam->list, &pas->lh);
                spin_unlock_irqrestore(&pas->lock, flags);
        } else {                /* Remove */
                spin_lock_irqsave(&pas->lock, flags);
                list_for_each_entry(pam, &pas->lh, list) {
                        if (pam->page == page) {
                                list_del(&pam->list);
                                spin_unlock_irqrestore(&pas->lock, flags);
                                goto done;
                        }
                }
                spin_unlock_irqrestore(&pas->lock, flags);
        }
done:
        return;
}

void __init page_address_init(void)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
                INIT_LIST_HEAD(&page_address_htable[i].lh);
                spin_lock_init(&page_address_htable[i].lock);
        }
}

#endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */