/*
 *  mm/userfaultfd.c
 *
 *  Copyright (C) 2015  Red Hat, Inc.
 *
 *  This work is licensed under the terms of the GNU GPL, version 2. See
 *  the COPYING file in the top-level directory.
 */

#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/userfaultfd_k.h>
#include <linux/mmu_notifier.h>
#include <asm/tlbflush.h>
#include "internal.h"

static int mcopy_atomic_pte(struct mm_struct *dst_mm,
                            pmd_t *dst_pmd,
                            struct vm_area_struct *dst_vma,
                            unsigned long dst_addr,
                            unsigned long src_addr,
                            struct page **pagep)
{
        struct mem_cgroup *memcg;
        pte_t _dst_pte, *dst_pte;
        spinlock_t *ptl;
        void *page_kaddr;
        int ret;
        struct page *page;

        if (!*pagep) {
                ret = -ENOMEM;
                page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
                if (!page)
                        goto out;

                page_kaddr = kmap_atomic(page);
                ret = copy_from_user(page_kaddr,
                                     (const void __user *) src_addr,
                                     PAGE_SIZE);
                kunmap_atomic(page_kaddr);

                /* fallback to copy_from_user outside mmap_sem */
                if (unlikely(ret)) {
                        ret = -EFAULT;
                        *pagep = page;
                        /* don't free the page */
                        goto out;
                }
        } else {
                page = *pagep;
                *pagep = NULL;
        }

        /*
         * The memory barrier inside __SetPageUptodate makes sure that
         * preceeding stores to the page contents become visible before
         * the set_pte_at() write.
         */
        __SetPageUptodate(page);

        ret = -ENOMEM;
        if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg))
                goto out_release;

        _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
        if (dst_vma->vm_flags & VM_WRITE)
                _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

        ret = -EEXIST;
        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
        if (!pte_none(*dst_pte))
                goto out_release_uncharge_unlock;

        inc_mm_counter(dst_mm, MM_ANONPAGES);
        page_add_new_anon_rmap(page, dst_vma, dst_addr);
        mem_cgroup_commit_charge(page, memcg, false);
        lru_cache_add_active_or_unevictable(page, dst_vma);

        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);

        pte_unmap_unlock(dst_pte, ptl);
        ret = 0;
out:
        return ret;
out_release_uncharge_unlock:
        pte_unmap_unlock(dst_pte, ptl);
        mem_cgroup_cancel_charge(page, memcg);
out_release:
        page_cache_release(page);
        goto out;
}

static int mfill_zeropage_pte(struct mm_struct *dst_mm,
                              pmd_t *dst_pmd,
                              struct vm_area_struct *dst_vma,
                              unsigned long dst_addr)
{
        pte_t _dst_pte, *dst_pte;
        spinlock_t *ptl;
        int ret;

        _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
                                         dst_vma->vm_page_prot));
        ret = -EEXIST;
        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
        if (!pte_none(*dst_pte))
                goto out_unlock;
        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        ret = 0;
out_unlock:
        pte_unmap_unlock(dst_pte, ptl);
        return ret;
}

static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd = NULL;

        pgd = pgd_offset(mm, address);
        pud = pud_alloc(mm, pgd, address);
        if (pud)
                /*
                 * Note that we didn't run this because the pmd was
                 * missing, the *pmd may be already established and in
                 * turn it may also be a trans_huge_pmd.
                 */
                pmd = pmd_alloc(mm, pud, address);
        return pmd;
}

static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
                                              unsigned long dst_start,
                                              unsigned long src_start,
                                              unsigned long len,
                                              bool zeropage)
{
        struct vm_area_struct *dst_vma;
        ssize_t err;
        pmd_t *dst_pmd;
        unsigned long src_addr, dst_addr;
        long copied;
        struct page *page;

        /*
         * Sanitize the command parameters:
         */
        BUG_ON(dst_start & ~PAGE_MASK);
        BUG_ON(len & ~PAGE_MASK);

        /* Does the address range wrap, or is the span zero-sized? */
        BUG_ON(src_start + len <= src_start);
        BUG_ON(dst_start + len <= dst_start);

        src_addr = src_start;
        dst_addr = dst_start;
        copied = 0;
        page = NULL;
retry:
        down_read(&dst_mm->mmap_sem);

        /*
         * Make sure the vma is not shared, that the dst range is
         * both valid and fully within a single existing vma.
         */
        err = -EINVAL;
        dst_vma = find_vma(dst_mm, dst_start);
        if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
                goto out_unlock;
        if (dst_start < dst_vma->vm_start ||
            dst_start + len > dst_vma->vm_end)
                goto out_unlock;

        /*
         * Be strict and only allow __mcopy_atomic on userfaultfd
         * registered ranges to prevent userland errors going
         * unnoticed. As far as the VM consistency is concerned, it
         * would be perfectly safe to remove this check, but there's
         * no useful usage for __mcopy_atomic ouside of userfaultfd
         * registered ranges. This is after all why these are ioctls
         * belonging to the userfaultfd and not syscalls.
         */
        if (!dst_vma->vm_userfaultfd_ctx.ctx)
                goto out_unlock;

        /*
         * FIXME: only allow copying on anonymous vmas, tmpfs should
         * be added.
         */
        if (dst_vma->vm_ops)
                goto out_unlock;

        /*
         * Ensure the dst_vma has a anon_vma or this page
         * would get a NULL anon_vma when moved in the
         * dst_vma.
         */
        err = -ENOMEM;
        if (unlikely(anon_vma_prepare(dst_vma)))
                goto out_unlock;

        while (src_addr < src_start + len) {
                pmd_t dst_pmdval;

                BUG_ON(dst_addr >= dst_start + len);

                dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
                if (unlikely(!dst_pmd)) {
                        err = -ENOMEM;
                        break;
                }

                dst_pmdval = pmd_read_atomic(dst_pmd);
                /*
                 * If the dst_pmd is mapped as THP don't
                 * override it and just be strict.
                 */
                if (unlikely(pmd_trans_huge(dst_pmdval))) {
                        err = -EEXIST;
                        break;
                }
                if (unlikely(pmd_none(dst_pmdval)) &&
                    unlikely(__pte_alloc(dst_mm, dst_vma, dst_pmd,
                                         dst_addr))) {
                        err = -ENOMEM;
                        break;
                }
                /* If an huge pmd materialized from under us fail */
                if (unlikely(pmd_trans_huge(*dst_pmd))) {
                        err = -EFAULT;
                        break;
                }

                BUG_ON(pmd_none(*dst_pmd));
                BUG_ON(pmd_trans_huge(*dst_pmd));

                if (!zeropage)
                        err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
                                               dst_addr, src_addr, &page);
                else
                        err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
                                                 dst_addr);

                cond_resched();

                if (unlikely(err == -EFAULT)) {
                        void *page_kaddr;

                        up_read(&dst_mm->mmap_sem);
                        BUG_ON(!page);

                        page_kaddr = kmap(page);
                        err = copy_from_user(page_kaddr,
                                             (const void __user *) src_addr,
                                             PAGE_SIZE);
                        kunmap(page);
                        if (unlikely(err)) {
                                err = -EFAULT;
                                goto out;
                        }
                        goto retry;
                } else
                        BUG_ON(page);

                if (!err) {
                        dst_addr += PAGE_SIZE;
                        src_addr += PAGE_SIZE;
                        copied += PAGE_SIZE;

                        if (fatal_signal_pending(current))
                                err = -EINTR;
                }
                if (err)
                        break;
        }

out_unlock:
        up_read(&dst_mm->mmap_sem);
out:
        if (page)
                page_cache_release(page);
        BUG_ON(copied < 0);
        BUG_ON(err > 0);
        BUG_ON(!copied && !err);
        return copied ? copied : err;
}

ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
                     unsigned long src_start, unsigned long len)
{
        return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
}

ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
                       unsigned long len)
{
        return __mcopy_atomic(dst_mm, start, 0, len, true);
}