// SPDX-License-Identifier: GPL-2.0

/*
 *  Handling Page Tables through page fragments
 *
 */

#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/hugetlb.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>

void pte_frag_destroy(void *pte_frag)
{
        int count;
        struct ptdesc *ptdesc;

        ptdesc = virt_to_ptdesc(pte_frag);
        /* drop all the pending references */
        count = ((unsigned long)pte_frag & ~PAGE_MASK) >> PTE_FRAG_SIZE_SHIFT;
        /* We allow PTE_FRAG_NR fragments from a PTE page */
        if (atomic_sub_and_test(PTE_FRAG_NR - count, &ptdesc->pt_frag_refcount)) {
                pagetable_dtor(ptdesc);
                pagetable_free(ptdesc);
        }
}

static pte_t *get_pte_from_cache(struct mm_struct *mm)
{
        void *pte_frag, *ret;

        if (PTE_FRAG_NR == 1)
                return NULL;

        spin_lock(&mm->page_table_lock);
        ret = pte_frag_get(&mm->context);
        if (ret) {
                pte_frag = ret + PTE_FRAG_SIZE;
                /*
                 * If we have taken up all the fragments mark PTE page NULL
                 */
                if (((unsigned long)pte_frag & ~PAGE_MASK) == 0)
                        pte_frag = NULL;
                pte_frag_set(&mm->context, pte_frag);
        }
        spin_unlock(&mm->page_table_lock);
        return (pte_t *)ret;
}

static pte_t *__alloc_for_ptecache(struct mm_struct *mm, int kernel)
{
        void *ret = NULL;
        struct ptdesc *ptdesc;
        gfp_t gfp = PGALLOC_GFP;

        if (!kernel)
                gfp |= __GFP_ACCOUNT;

        ptdesc = pagetable_alloc(gfp, 0);
        if (!ptdesc)
                return NULL;
        if (!pagetable_pte_ctor(mm, ptdesc)) {
                pagetable_free(ptdesc);
                return NULL;
        }

        atomic_set(&ptdesc->pt_frag_refcount, 1);

        ret = ptdesc_address(ptdesc);
        /*
         * if we support only one fragment just return the
         * allocated page.
         */
        if (PTE_FRAG_NR == 1)
                return ret;
        spin_lock(&mm->page_table_lock);
        /*
         * If we find ptdesc_page set, we return
         * the allocated page with single fragment
         * count.
         */
        if (likely(!pte_frag_get(&mm->context))) {
                atomic_set(&ptdesc->pt_frag_refcount, PTE_FRAG_NR);
                pte_frag_set(&mm->context, ret + PTE_FRAG_SIZE);
        }
        spin_unlock(&mm->page_table_lock);

        return (pte_t *)ret;
}

pte_t *pte_fragment_alloc(struct mm_struct *mm, int kernel)
{
        pte_t *pte;

        pte = get_pte_from_cache(mm);
        if (pte)
                return pte;

        return __alloc_for_ptecache(mm, kernel);
}

static void pte_free_now(struct rcu_head *head)
{
        struct ptdesc *ptdesc;

        ptdesc = container_of(head, struct ptdesc, pt_rcu_head);
        pagetable_dtor(ptdesc);
        pagetable_free(ptdesc);
}

void pte_fragment_free(unsigned long *table, int kernel)
{
        struct ptdesc *ptdesc = virt_to_ptdesc(table);

        if (pagetable_is_reserved(ptdesc))
                return free_reserved_ptdesc(ptdesc);

        BUG_ON(atomic_read(&ptdesc->pt_frag_refcount) <= 0);
        if (atomic_dec_and_test(&ptdesc->pt_frag_refcount)) {
                if (kernel || !folio_test_clear_active(ptdesc_folio(ptdesc)))
                        pte_free_now(&ptdesc->pt_rcu_head);
                else
                        call_rcu(&ptdesc->pt_rcu_head, pte_free_now);
        }
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
{
        struct folio *folio;

        folio = virt_to_folio(pgtable);
        folio_set_active(folio);
        pte_fragment_free((unsigned long *)pgtable, 0);
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */