/*
 *  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/sched/signal.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 <linux/hugetlb.h>
#include <linux/shmem_fs.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, false))
                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, false);
        mem_cgroup_commit_charge(page, memcg, false, 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, false);
out_release:
        put_page(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;
        p4d_t *p4d;
        pud_t *pud;

        pgd = pgd_offset(mm, address);
        p4d = p4d_alloc(mm, pgd, address);
        if (!p4d)
                return NULL;
        pud = pud_alloc(mm, p4d, address);
        if (!pud)
                return NULL;
        /*
         * 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.
         */
        return pmd_alloc(mm, pud, address);
}

#ifdef CONFIG_HUGETLB_PAGE
/*
 * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
 * called with mmap_sem held, it will release mmap_sem before returning.
 */
static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
                                              struct vm_area_struct *dst_vma,
                                              unsigned long dst_start,
                                              unsigned long src_start,
                                              unsigned long len,
                                              bool zeropage)
{
        int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
        int vm_shared = dst_vma->vm_flags & VM_SHARED;
        ssize_t err;
        pte_t *dst_pte;
        unsigned long src_addr, dst_addr;
        long copied;
        struct page *page;
        struct hstate *h;
        unsigned long vma_hpagesize;
        pgoff_t idx;
        u32 hash;
        struct address_space *mapping;

        /*
         * There is no default zero huge page for all huge page sizes as
         * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
         * by THP.  Since we can not reliably insert a zero page, this
         * feature is not supported.
         */
        if (zeropage) {
                up_read(&dst_mm->mmap_sem);
                return -EINVAL;
        }

        src_addr = src_start;
        dst_addr = dst_start;
        copied = 0;
        page = NULL;
        vma_hpagesize = vma_kernel_pagesize(dst_vma);

        /*
         * Validate alignment based on huge page size
         */
        err = -EINVAL;
        if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
                goto out_unlock;

retry:
        /*
         * On routine entry dst_vma is set.  If we had to drop mmap_sem and
         * retry, dst_vma will be set to NULL and we must lookup again.
         */
        if (!dst_vma) {
                err = -ENOENT;
                dst_vma = find_vma(dst_mm, dst_start);
                if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
                        goto out_unlock;
                /*
                 * Only allow __mcopy_atomic_hugetlb on userfaultfd
                 * registered ranges.
                 */
                if (!dst_vma->vm_userfaultfd_ctx.ctx)
                        goto out_unlock;

                if (dst_start < dst_vma->vm_start ||
                    dst_start + len > dst_vma->vm_end)
                        goto out_unlock;

                err = -EINVAL;
                if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
                        goto out_unlock;

                vm_shared = dst_vma->vm_flags & VM_SHARED;
        }

        if (WARN_ON(dst_addr & (vma_hpagesize - 1) ||
                    (len - copied) & (vma_hpagesize - 1)))
                goto out_unlock;

        /*
         * If not shared, ensure the dst_vma has a anon_vma.
         */
        err = -ENOMEM;
        if (!vm_shared) {
                if (unlikely(anon_vma_prepare(dst_vma)))
                        goto out_unlock;
        }

        h = hstate_vma(dst_vma);

        while (src_addr < src_start + len) {
                pte_t dst_pteval;

                BUG_ON(dst_addr >= dst_start + len);
                VM_BUG_ON(dst_addr & ~huge_page_mask(h));

                /*
                 * Serialize via hugetlb_fault_mutex
                 */
                idx = linear_page_index(dst_vma, dst_addr);
                mapping = dst_vma->vm_file->f_mapping;
                hash = hugetlb_fault_mutex_hash(h, dst_mm, dst_vma, mapping,
                                                                idx, dst_addr);
                mutex_lock(&hugetlb_fault_mutex_table[hash]);

                err = -ENOMEM;
                dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
                if (!dst_pte) {
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        goto out_unlock;
                }

                err = -EEXIST;
                dst_pteval = huge_ptep_get(dst_pte);
                if (!huge_pte_none(dst_pteval)) {
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        goto out_unlock;
                }

                err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
                                                dst_addr, src_addr, &page);

                mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                vm_alloc_shared = vm_shared;

                cond_resched();

                if (unlikely(err == -EFAULT)) {
                        up_read(&dst_mm->mmap_sem);
                        BUG_ON(!page);

                        err = copy_huge_page_from_user(page,
                                                (const void __user *)src_addr,
                                                pages_per_huge_page(h), true);
                        if (unlikely(err)) {
                                err = -EFAULT;
                                goto out;
                        }
                        down_read(&dst_mm->mmap_sem);

                        dst_vma = NULL;
                        goto retry;
                } else
                        BUG_ON(page);

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

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

out_unlock:
        up_read(&dst_mm->mmap_sem);
out:
        if (page) {
                /*
                 * We encountered an error and are about to free a newly
                 * allocated huge page.
                 *
                 * Reservation handling is very subtle, and is different for
                 * private and shared mappings.  See the routine
                 * restore_reserve_on_error for details.  Unfortunately, we
                 * can not call restore_reserve_on_error now as it would
                 * require holding mmap_sem.
                 *
                 * If a reservation for the page existed in the reservation
                 * map of a private mapping, the map was modified to indicate
                 * the reservation was consumed when the page was allocated.
                 * We clear the PagePrivate flag now so that the global
                 * reserve count will not be incremented in free_huge_page.
                 * The reservation map will still indicate the reservation
                 * was consumed and possibly prevent later page allocation.
                 * This is better than leaking a global reservation.  If no
                 * reservation existed, it is still safe to clear PagePrivate
                 * as no adjustments to reservation counts were made during
                 * allocation.
                 *
                 * The reservation map for shared mappings indicates which
                 * pages have reservations.  When a huge page is allocated
                 * for an address with a reservation, no change is made to
                 * the reserve map.  In this case PagePrivate will be set
                 * to indicate that the global reservation count should be
                 * incremented when the page is freed.  This is the desired
                 * behavior.  However, when a huge page is allocated for an
                 * address without a reservation a reservation entry is added
                 * to the reservation map, and PagePrivate will not be set.
                 * When the page is freed, the global reserve count will NOT
                 * be incremented and it will appear as though we have leaked
                 * reserved page.  In this case, set PagePrivate so that the
                 * global reserve count will be incremented to match the
                 * reservation map entry which was created.
                 *
                 * Note that vm_alloc_shared is based on the flags of the vma
                 * for which the page was originally allocated.  dst_vma could
                 * be different or NULL on error.
                 */
                if (vm_alloc_shared)
                        SetPagePrivate(page);
                else
                        ClearPagePrivate(page);
                put_page(page);
        }
        BUG_ON(copied < 0);
        BUG_ON(err > 0);
        BUG_ON(!copied && !err);
        return copied ? copied : err;
}
#else /* !CONFIG_HUGETLB_PAGE */
/* fail at build time if gcc attempts to use this */
extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
                                      struct vm_area_struct *dst_vma,
                                      unsigned long dst_start,
                                      unsigned long src_start,
                                      unsigned long len,
                                      bool zeropage);
#endif /* CONFIG_HUGETLB_PAGE */

static __always_inline ssize_t mfill_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 **page,
                                                bool zeropage)
{
        ssize_t err;

        if (vma_is_anonymous(dst_vma)) {
                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);
        } else {
                if (!zeropage)
                        err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
                                                     dst_vma, dst_addr,
                                                     src_addr, page);
                else
                        err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd,
                                                       dst_vma, dst_addr);
        }

        return err;
}

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 = -ENOENT;
        dst_vma = find_vma(dst_mm, dst_start);
        if (!dst_vma)
                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;

        if (dst_start < dst_vma->vm_start ||
            dst_start + len > dst_vma->vm_end)
                goto out_unlock;

        err = -EINVAL;
        /*
         * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
         * it will overwrite vm_ops, so vma_is_anonymous must return false.
         */
        if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
            dst_vma->vm_flags & VM_SHARED))
                goto out_unlock;

        /*
         * If this is a HUGETLB vma, pass off to appropriate routine
         */
        if (is_vm_hugetlb_page(dst_vma))
                return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
                                                src_start, len, zeropage);

        if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
                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 (vma_is_anonymous(dst_vma) && 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_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));

                err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
                                       src_addr, &page, zeropage);
                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)
                put_page(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);
}