/*
 *  Page table allocation functions
 *
 *    Copyright IBM Corp. 2016
 *    Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
 */

#include <linux/mm.h>
#include <linux/sysctl.h>
#include <asm/mmu_context.h>
#include <asm/pgalloc.h>
#include <asm/gmap.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>

#ifdef CONFIG_PGSTE

static int page_table_allocate_pgste_min = 0;
static int page_table_allocate_pgste_max = 1;
int page_table_allocate_pgste = 0;
EXPORT_SYMBOL(page_table_allocate_pgste);

static struct ctl_table page_table_sysctl[] = {
        {
                .procname       = "allocate_pgste",
                .data           = &page_table_allocate_pgste,
                .maxlen         = sizeof(int),
                .mode           = S_IRUGO | S_IWUSR,
                .proc_handler   = proc_dointvec,
                .extra1         = &page_table_allocate_pgste_min,
                .extra2         = &page_table_allocate_pgste_max,
        },
        { }
};

static struct ctl_table page_table_sysctl_dir[] = {
        {
                .procname       = "vm",
                .maxlen         = 0,
                .mode           = 0555,
                .child          = page_table_sysctl,
        },
        { }
};

static int __init page_table_register_sysctl(void)
{
        return register_sysctl_table(page_table_sysctl_dir) ? 0 : -ENOMEM;
}
__initcall(page_table_register_sysctl);

#endif /* CONFIG_PGSTE */

unsigned long *crst_table_alloc(struct mm_struct *mm)
{
        struct page *page = alloc_pages(GFP_KERNEL, 2);

        if (!page)
                return NULL;
        return (unsigned long *) page_to_phys(page);
}

void crst_table_free(struct mm_struct *mm, unsigned long *table)
{
        free_pages((unsigned long) table, 2);
}

static void __crst_table_upgrade(void *arg)
{
        struct mm_struct *mm = arg;

        if (current->active_mm == mm) {
                clear_user_asce();
                set_user_asce(mm);
        }
        __tlb_flush_local();
}

int crst_table_upgrade(struct mm_struct *mm)
{
        unsigned long *table, *pgd;

        /* upgrade should only happen from 3 to 4 levels */
        BUG_ON(mm->context.asce_limit != (1UL << 42));

        table = crst_table_alloc(mm);
        if (!table)
                return -ENOMEM;

        spin_lock_bh(&mm->page_table_lock);
        pgd = (unsigned long *) mm->pgd;
        crst_table_init(table, _REGION2_ENTRY_EMPTY);
        pgd_populate(mm, (pgd_t *) table, (pud_t *) pgd);
        mm->pgd = (pgd_t *) table;
        mm->context.asce_limit = 1UL << 53;
        mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
                           _ASCE_USER_BITS | _ASCE_TYPE_REGION2;
        mm->task_size = mm->context.asce_limit;
        spin_unlock_bh(&mm->page_table_lock);

        on_each_cpu(__crst_table_upgrade, mm, 0);
        return 0;
}

void crst_table_downgrade(struct mm_struct *mm)
{
        pgd_t *pgd;

        /* downgrade should only happen from 3 to 2 levels (compat only) */
        BUG_ON(mm->context.asce_limit != (1UL << 42));

        if (current->active_mm == mm) {
                clear_user_asce();
                __tlb_flush_mm(mm);
        }

        pgd = mm->pgd;
        mm->pgd = (pgd_t *) (pgd_val(*pgd) & _REGION_ENTRY_ORIGIN);
        mm->context.asce_limit = 1UL << 31;
        mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
                           _ASCE_USER_BITS | _ASCE_TYPE_SEGMENT;
        mm->task_size = mm->context.asce_limit;
        crst_table_free(mm, (unsigned long *) pgd);

        if (current->active_mm == mm)
                set_user_asce(mm);
}

static inline unsigned int atomic_xor_bits(atomic_t *v, unsigned int bits)
{
        unsigned int old, new;

        do {
                old = atomic_read(v);
                new = old ^ bits;
        } while (atomic_cmpxchg(v, old, new) != old);
        return new;
}

#ifdef CONFIG_PGSTE

struct page *page_table_alloc_pgste(struct mm_struct *mm)
{
        struct page *page;
        unsigned long *table;

        page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
        if (page) {
                table = (unsigned long *) page_to_phys(page);
                clear_table(table, _PAGE_INVALID, PAGE_SIZE/2);
                clear_table(table + PTRS_PER_PTE, 0, PAGE_SIZE/2);
        }
        return page;
}

void page_table_free_pgste(struct page *page)
{
        __free_page(page);
}

#endif /* CONFIG_PGSTE */

/*
 * page table entry allocation/free routines.
 */
unsigned long *page_table_alloc(struct mm_struct *mm)
{
        unsigned long *table;
        struct page *page;
        unsigned int mask, bit;

        /* Try to get a fragment of a 4K page as a 2K page table */
        if (!mm_alloc_pgste(mm)) {
                table = NULL;
                spin_lock_bh(&mm->context.pgtable_lock);
                if (!list_empty(&mm->context.pgtable_list)) {
                        page = list_first_entry(&mm->context.pgtable_list,
                                                struct page, lru);
                        mask = atomic_read(&page->_mapcount);
                        mask = (mask | (mask >> 4)) & 3;
                        if (mask != 3) {
                                table = (unsigned long *) page_to_phys(page);
                                bit = mask & 1;         /* =1 -> second 2K */
                                if (bit)
                                        table += PTRS_PER_PTE;
                                atomic_xor_bits(&page->_mapcount, 1U << bit);
                                list_del(&page->lru);
                        }
                }
                spin_unlock_bh(&mm->context.pgtable_lock);
                if (table)
                        return table;
        }
        /* Allocate a fresh page */
        page = alloc_page(GFP_KERNEL);
        if (!page)
                return NULL;
        if (!pgtable_page_ctor(page)) {
                __free_page(page);
                return NULL;
        }
        /* Initialize page table */
        table = (unsigned long *) page_to_phys(page);
        if (mm_alloc_pgste(mm)) {
                /* Return 4K page table with PGSTEs */
                atomic_set(&page->_mapcount, 3);
                clear_table(table, _PAGE_INVALID, PAGE_SIZE/2);
                clear_table(table + PTRS_PER_PTE, 0, PAGE_SIZE/2);
        } else {
                /* Return the first 2K fragment of the page */
                atomic_set(&page->_mapcount, 1);
                clear_table(table, _PAGE_INVALID, PAGE_SIZE);
                spin_lock_bh(&mm->context.pgtable_lock);
                list_add(&page->lru, &mm->context.pgtable_list);
                spin_unlock_bh(&mm->context.pgtable_lock);
        }
        return table;
}

void page_table_free(struct mm_struct *mm, unsigned long *table)
{
        struct page *page;
        unsigned int bit, mask;

        page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
        if (!mm_alloc_pgste(mm)) {
                /* Free 2K page table fragment of a 4K page */
                bit = (__pa(table) & ~PAGE_MASK)/(PTRS_PER_PTE*sizeof(pte_t));
                spin_lock_bh(&mm->context.pgtable_lock);
                mask = atomic_xor_bits(&page->_mapcount, 1U << bit);
                if (mask & 3)
                        list_add(&page->lru, &mm->context.pgtable_list);
                else
                        list_del(&page->lru);
                spin_unlock_bh(&mm->context.pgtable_lock);
                if (mask != 0)
                        return;
        }

        pgtable_page_dtor(page);
        atomic_set(&page->_mapcount, -1);
        __free_page(page);
}

void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table,
                         unsigned long vmaddr)
{
        struct mm_struct *mm;
        struct page *page;
        unsigned int bit, mask;

        mm = tlb->mm;
        page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
        if (mm_alloc_pgste(mm)) {
                gmap_unlink(mm, table, vmaddr);
                table = (unsigned long *) (__pa(table) | 3);
                tlb_remove_table(tlb, table);
                return;
        }
        bit = (__pa(table) & ~PAGE_MASK) / (PTRS_PER_PTE*sizeof(pte_t));
        spin_lock_bh(&mm->context.pgtable_lock);
        mask = atomic_xor_bits(&page->_mapcount, 0x11U << bit);
        if (mask & 3)
                list_add_tail(&page->lru, &mm->context.pgtable_list);
        else
                list_del(&page->lru);
        spin_unlock_bh(&mm->context.pgtable_lock);
        table = (unsigned long *) (__pa(table) | (1U << bit));
        tlb_remove_table(tlb, table);
}

static void __tlb_remove_table(void *_table)
{
        unsigned int mask = (unsigned long) _table & 3;
        void *table = (void *)((unsigned long) _table ^ mask);
        struct page *page = pfn_to_page(__pa(table) >> PAGE_SHIFT);

        switch (mask) {
        case 0:         /* pmd or pud */
                free_pages((unsigned long) table, 2);
                break;
        case 1:         /* lower 2K of a 4K page table */
        case 2:         /* higher 2K of a 4K page table */
                if (atomic_xor_bits(&page->_mapcount, mask << 4) != 0)
                        break;
                /* fallthrough */
        case 3:         /* 4K page table with pgstes */
                pgtable_page_dtor(page);
                atomic_set(&page->_mapcount, -1);
                __free_page(page);
                break;
        }
}

static void tlb_remove_table_smp_sync(void *arg)
{
        /* Simply deliver the interrupt */
}

static void tlb_remove_table_one(void *table)
{
        /*
         * This isn't an RCU grace period and hence the page-tables cannot be
         * assumed to be actually RCU-freed.
         *
         * It is however sufficient for software page-table walkers that rely
         * on IRQ disabling. See the comment near struct mmu_table_batch.
         */
        smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
        __tlb_remove_table(table);
}

static void tlb_remove_table_rcu(struct rcu_head *head)
{
        struct mmu_table_batch *batch;
        int i;

        batch = container_of(head, struct mmu_table_batch, rcu);

        for (i = 0; i < batch->nr; i++)
                __tlb_remove_table(batch->tables[i]);

        free_page((unsigned long)batch);
}

void tlb_table_flush(struct mmu_gather *tlb)
{
        struct mmu_table_batch **batch = &tlb->batch;

        if (*batch) {
                call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
                *batch = NULL;
        }
}

void tlb_remove_table(struct mmu_gather *tlb, void *table)
{
        struct mmu_table_batch **batch = &tlb->batch;

        tlb->mm->context.flush_mm = 1;
        if (*batch == NULL) {
                *batch = (struct mmu_table_batch *)
                        __get_free_page(GFP_NOWAIT | __GFP_NOWARN);
                if (*batch == NULL) {
                        __tlb_flush_mm_lazy(tlb->mm);
                        tlb_remove_table_one(table);
                        return;
                }
                (*batch)->nr = 0;
        }
        (*batch)->tables[(*batch)->nr++] = table;
        if ((*batch)->nr == MAX_TABLE_BATCH)
                tlb_flush_mmu(tlb);
}