/*
 * Copyright 2013 Red Hat Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * Authors: Jérôme Glisse <jglisse@redhat.com>
 */
/*
 * Refer to include/linux/hmm.h for information about heterogeneous memory
 * management or HMM for short.
 */
#include <linux/pagewalk.h>
#include <linux/hmm.h>
#include <linux/init.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/mmzone.h>
#include <linux/pagemap.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
#include <linux/memremap.h>
#include <linux/sched/mm.h>
#include <linux/jump_label.h>
#include <linux/dma-mapping.h>
#include <linux/mmu_notifier.h>
#include <linux/memory_hotplug.h>

struct hmm_vma_walk {
        struct hmm_range        *range;
        unsigned long           last;
};

enum {
        HMM_NEED_FAULT = 1 << 0,
        HMM_NEED_WRITE_FAULT = 1 << 1,
        HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
};

static int hmm_pfns_fill(unsigned long addr, unsigned long end,
                         struct hmm_range *range, unsigned long cpu_flags)
{
        unsigned long i = (addr - range->start) >> PAGE_SHIFT;

        for (; addr < end; addr += PAGE_SIZE, i++)
                range->hmm_pfns[i] = cpu_flags;
        return 0;
}

/*
 * hmm_vma_fault() - fault in a range lacking valid pmd or pte(s)
 * @addr: range virtual start address (inclusive)
 * @end: range virtual end address (exclusive)
 * @required_fault: HMM_NEED_* flags
 * @walk: mm_walk structure
 * Return: -EBUSY after page fault, or page fault error
 *
 * This function will be called whenever pmd_none() or pte_none() returns true,
 * or whenever there is no page directory covering the virtual address range.
 */
static int hmm_vma_fault(unsigned long addr, unsigned long end,
                         unsigned int required_fault, struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct vm_area_struct *vma = walk->vma;
        unsigned int fault_flags = FAULT_FLAG_REMOTE;

        WARN_ON_ONCE(!required_fault);
        hmm_vma_walk->last = addr;

        if (required_fault & HMM_NEED_WRITE_FAULT) {
                if (!(vma->vm_flags & VM_WRITE))
                        return -EPERM;
                fault_flags |= FAULT_FLAG_WRITE;
        }

        for (; addr < end; addr += PAGE_SIZE)
                if (handle_mm_fault(vma, addr, fault_flags) & VM_FAULT_ERROR)
                        return -EFAULT;
        return -EBUSY;
}

static unsigned int hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
                                       unsigned long pfn_req_flags,
                                       unsigned long cpu_flags)
{
        struct hmm_range *range = hmm_vma_walk->range;

        /*
         * So we not only consider the individual per page request we also
         * consider the default flags requested for the range. The API can
         * be used 2 ways. The first one where the HMM user coalesces
         * multiple page faults into one request and sets flags per pfn for
         * those faults. The second one where the HMM user wants to pre-
         * fault a range with specific flags. For the latter one it is a
         * waste to have the user pre-fill the pfn arrays with a default
         * flags value.
         */
        pfn_req_flags &= range->pfn_flags_mask;
        pfn_req_flags |= range->default_flags;

        /* We aren't ask to do anything ... */
        if (!(pfn_req_flags & HMM_PFN_REQ_FAULT))
                return 0;

        /* Need to write fault ? */
        if ((pfn_req_flags & HMM_PFN_REQ_WRITE) &&
            !(cpu_flags & HMM_PFN_WRITE))
                return HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT;

        /* If CPU page table is not valid then we need to fault */
        if (!(cpu_flags & HMM_PFN_VALID))
                return HMM_NEED_FAULT;
        return 0;
}

static unsigned int
hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
                     const unsigned long hmm_pfns[], unsigned long npages,
                     unsigned long cpu_flags)
{
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned int required_fault = 0;
        unsigned long i;

        /*
         * If the default flags do not request to fault pages, and the mask does
         * not allow for individual pages to be faulted, then
         * hmm_pte_need_fault() will always return 0.
         */
        if (!((range->default_flags | range->pfn_flags_mask) &
              HMM_PFN_REQ_FAULT))
                return 0;

        for (i = 0; i < npages; ++i) {
                required_fault |= hmm_pte_need_fault(hmm_vma_walk, hmm_pfns[i],
                                                     cpu_flags);
                if (required_fault == HMM_NEED_ALL_BITS)
                        return required_fault;
        }
        return required_fault;
}

static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
                             __always_unused int depth, struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned int required_fault;
        unsigned long i, npages;
        unsigned long *hmm_pfns;

        i = (addr - range->start) >> PAGE_SHIFT;
        npages = (end - addr) >> PAGE_SHIFT;
        hmm_pfns = &range->hmm_pfns[i];
        required_fault =
                hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0);
        if (!walk->vma) {
                if (required_fault)
                        return -EFAULT;
                return hmm_pfns_fill(addr, end, range, HMM_PFN_ERROR);
        }
        if (required_fault)
                return hmm_vma_fault(addr, end, required_fault, walk);
        return hmm_pfns_fill(addr, end, range, 0);
}

static inline unsigned long hmm_pfn_flags_order(unsigned long order)
{
        return order << HMM_PFN_ORDER_SHIFT;
}

static inline unsigned long pmd_to_hmm_pfn_flags(struct hmm_range *range,
                                                 pmd_t pmd)
{
        if (pmd_protnone(pmd))
                return 0;
        return (pmd_write(pmd) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
                                 HMM_PFN_VALID) |
               hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
                              unsigned long end, unsigned long hmm_pfns[],
                              pmd_t pmd)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned long pfn, npages, i;
        unsigned int required_fault;
        unsigned long cpu_flags;

        npages = (end - addr) >> PAGE_SHIFT;
        cpu_flags = pmd_to_hmm_pfn_flags(range, pmd);
        required_fault =
                hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, cpu_flags);
        if (required_fault)
                return hmm_vma_fault(addr, end, required_fault, walk);

        pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
        for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
                hmm_pfns[i] = pfn | cpu_flags;
        return 0;
}
#else /* CONFIG_TRANSPARENT_HUGEPAGE */
/* stub to allow the code below to compile */
int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
                unsigned long end, unsigned long hmm_pfns[], pmd_t pmd);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

static inline bool hmm_is_device_private_entry(struct hmm_range *range,
                swp_entry_t entry)
{
        return is_device_private_entry(entry) &&
                device_private_entry_to_page(entry)->pgmap->owner ==
                range->dev_private_owner;
}

static inline unsigned long pte_to_hmm_pfn_flags(struct hmm_range *range,
                                                 pte_t pte)
{
        if (pte_none(pte) || !pte_present(pte) || pte_protnone(pte))
                return 0;
        return pte_write(pte) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
}

static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
                              unsigned long end, pmd_t *pmdp, pte_t *ptep,
                              unsigned long *hmm_pfn)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned int required_fault;
        unsigned long cpu_flags;
        pte_t pte = *ptep;
        uint64_t pfn_req_flags = *hmm_pfn;

        if (pte_none(pte)) {
                required_fault =
                        hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
                if (required_fault)
                        goto fault;
                *hmm_pfn = 0;
                return 0;
        }

        if (!pte_present(pte)) {
                swp_entry_t entry = pte_to_swp_entry(pte);

                /*
                 * Never fault in device private pages, but just report
                 * the PFN even if not present.
                 */
                if (hmm_is_device_private_entry(range, entry)) {
                        cpu_flags = HMM_PFN_VALID;
                        if (is_write_device_private_entry(entry))
                                cpu_flags |= HMM_PFN_WRITE;
                        *hmm_pfn = device_private_entry_to_pfn(entry) |
                                        cpu_flags;
                        return 0;
                }

                required_fault =
                        hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
                if (!required_fault) {
                        *hmm_pfn = 0;
                        return 0;
                }

                if (!non_swap_entry(entry))
                        goto fault;

                if (is_migration_entry(entry)) {
                        pte_unmap(ptep);
                        hmm_vma_walk->last = addr;
                        migration_entry_wait(walk->mm, pmdp, addr);
                        return -EBUSY;
                }

                /* Report error for everything else */
                pte_unmap(ptep);
                return -EFAULT;
        }

        cpu_flags = pte_to_hmm_pfn_flags(range, pte);
        required_fault =
                hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
        if (required_fault)
                goto fault;

        /*
         * Since each architecture defines a struct page for the zero page, just
         * fall through and treat it like a normal page.
         */
        if (pte_special(pte) && !is_zero_pfn(pte_pfn(pte))) {
                if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
                        pte_unmap(ptep);
                        return -EFAULT;
                }
                *hmm_pfn = HMM_PFN_ERROR;
                return 0;
        }

        *hmm_pfn = pte_pfn(pte) | cpu_flags;
        return 0;

fault:
        pte_unmap(ptep);
        /* Fault any virtual address we were asked to fault */
        return hmm_vma_fault(addr, end, required_fault, walk);
}

static int hmm_vma_walk_pmd(pmd_t *pmdp,
                            unsigned long start,
                            unsigned long end,
                            struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned long *hmm_pfns =
                &range->hmm_pfns[(start - range->start) >> PAGE_SHIFT];
        unsigned long npages = (end - start) >> PAGE_SHIFT;
        unsigned long addr = start;
        pte_t *ptep;
        pmd_t pmd;

again:
        pmd = READ_ONCE(*pmdp);
        if (pmd_none(pmd))
                return hmm_vma_walk_hole(start, end, -1, walk);

        if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
                if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) {
                        hmm_vma_walk->last = addr;
                        pmd_migration_entry_wait(walk->mm, pmdp);
                        return -EBUSY;
                }
                return hmm_pfns_fill(start, end, range, 0);
        }

        if (!pmd_present(pmd)) {
                if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
                        return -EFAULT;
                return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
        }

        if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {
                /*
                 * No need to take pmd_lock here, even if some other thread
                 * is splitting the huge pmd we will get that event through
                 * mmu_notifier callback.
                 *
                 * So just read pmd value and check again it's a transparent
                 * huge or device mapping one and compute corresponding pfn
                 * values.
                 */
                pmd = pmd_read_atomic(pmdp);
                barrier();
                if (!pmd_devmap(pmd) && !pmd_trans_huge(pmd))
                        goto again;

                return hmm_vma_handle_pmd(walk, addr, end, hmm_pfns, pmd);
        }

        /*
         * We have handled all the valid cases above ie either none, migration,
         * huge or transparent huge. At this point either it is a valid pmd
         * entry pointing to pte directory or it is a bad pmd that will not
         * recover.
         */
        if (pmd_bad(pmd)) {
                if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
                        return -EFAULT;
                return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
        }

        ptep = pte_offset_map(pmdp, addr);
        for (; addr < end; addr += PAGE_SIZE, ptep++, hmm_pfns++) {
                int r;

                r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, hmm_pfns);
                if (r) {
                        /* hmm_vma_handle_pte() did pte_unmap() */
                        return r;
                }
        }
        pte_unmap(ptep - 1);
        return 0;
}

#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
    defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
static inline unsigned long pud_to_hmm_pfn_flags(struct hmm_range *range,
                                                 pud_t pud)
{
        if (!pud_present(pud))
                return 0;
        return (pud_write(pud) ? (HMM_PFN_VALID | HMM_PFN_WRITE) :
                                 HMM_PFN_VALID) |
               hmm_pfn_flags_order(PUD_SHIFT - PAGE_SHIFT);
}

static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
                struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        unsigned long addr = start;
        pud_t pud;
        int ret = 0;
        spinlock_t *ptl = pud_trans_huge_lock(pudp, walk->vma);

        if (!ptl)
                return 0;

        /* Normally we don't want to split the huge page */
        walk->action = ACTION_CONTINUE;

        pud = READ_ONCE(*pudp);
        if (pud_none(pud)) {
                spin_unlock(ptl);
                return hmm_vma_walk_hole(start, end, -1, walk);
        }

        if (pud_huge(pud) && pud_devmap(pud)) {
                unsigned long i, npages, pfn;
                unsigned int required_fault;
                unsigned long *hmm_pfns;
                unsigned long cpu_flags;

                if (!pud_present(pud)) {
                        spin_unlock(ptl);
                        return hmm_vma_walk_hole(start, end, -1, walk);
                }

                i = (addr - range->start) >> PAGE_SHIFT;
                npages = (end - addr) >> PAGE_SHIFT;
                hmm_pfns = &range->hmm_pfns[i];

                cpu_flags = pud_to_hmm_pfn_flags(range, pud);
                required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns,
                                                      npages, cpu_flags);
                if (required_fault) {
                        spin_unlock(ptl);
                        return hmm_vma_fault(addr, end, required_fault, walk);
                }

                pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
                for (i = 0; i < npages; ++i, ++pfn)
                        hmm_pfns[i] = pfn | cpu_flags;
                goto out_unlock;
        }

        /* Ask for the PUD to be split */
        walk->action = ACTION_SUBTREE;

out_unlock:
        spin_unlock(ptl);
        return ret;
}
#else
#define hmm_vma_walk_pud        NULL
#endif

#ifdef CONFIG_HUGETLB_PAGE
static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
                                      unsigned long start, unsigned long end,
                                      struct mm_walk *walk)
{
        unsigned long addr = start, i, pfn;
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        struct vm_area_struct *vma = walk->vma;
        unsigned int required_fault;
        unsigned long pfn_req_flags;
        unsigned long cpu_flags;
        spinlock_t *ptl;
        pte_t entry;

        ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
        entry = huge_ptep_get(pte);

        i = (start - range->start) >> PAGE_SHIFT;
        pfn_req_flags = range->hmm_pfns[i];
        cpu_flags = pte_to_hmm_pfn_flags(range, entry) |
                    hmm_pfn_flags_order(huge_page_order(hstate_vma(vma)));
        required_fault =
                hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, cpu_flags);
        if (required_fault) {
                spin_unlock(ptl);
                return hmm_vma_fault(addr, end, required_fault, walk);
        }

        pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
        for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
                range->hmm_pfns[i] = pfn | cpu_flags;

        spin_unlock(ptl);
        return 0;
}
#else
#define hmm_vma_walk_hugetlb_entry NULL
#endif /* CONFIG_HUGETLB_PAGE */

static int hmm_vma_walk_test(unsigned long start, unsigned long end,
                             struct mm_walk *walk)
{
        struct hmm_vma_walk *hmm_vma_walk = walk->private;
        struct hmm_range *range = hmm_vma_walk->range;
        struct vm_area_struct *vma = walk->vma;

        if (!(vma->vm_flags & (VM_IO | VM_PFNMAP | VM_MIXEDMAP)) &&
            vma->vm_flags & VM_READ)
                return 0;

        /*
         * vma ranges that don't have struct page backing them or map I/O
         * devices directly cannot be handled by hmm_range_fault().
         *
         * If the vma does not allow read access, then assume that it does not
         * allow write access either. HMM does not support architectures that
         * allow write without read.
         *
         * If a fault is requested for an unsupported range then it is a hard
         * failure.
         */
        if (hmm_range_need_fault(hmm_vma_walk,
                                 range->hmm_pfns +
                                         ((start - range->start) >> PAGE_SHIFT),
                                 (end - start) >> PAGE_SHIFT, 0))
                return -EFAULT;

        hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);

        /* Skip this vma and continue processing the next vma. */
        return 1;
}

static const struct mm_walk_ops hmm_walk_ops = {
        .pud_entry      = hmm_vma_walk_pud,
        .pmd_entry      = hmm_vma_walk_pmd,
        .pte_hole       = hmm_vma_walk_hole,
        .hugetlb_entry  = hmm_vma_walk_hugetlb_entry,
        .test_walk      = hmm_vma_walk_test,
};

/**
 * hmm_range_fault - try to fault some address in a virtual address range
 * @range:      argument structure
 *
 * Returns 0 on success or one of the following error codes:
 *
 * -EINVAL:     Invalid arguments or mm or virtual address is in an invalid vma
 *              (e.g., device file vma).
 * -ENOMEM:     Out of memory.
 * -EPERM:      Invalid permission (e.g., asking for write and range is read
 *              only).
 * -EBUSY:      The range has been invalidated and the caller needs to wait for
 *              the invalidation to finish.
 * -EFAULT:     A page was requested to be valid and could not be made valid
 *              ie it has no backing VMA or it is illegal to access
 *
 * This is similar to get_user_pages(), except that it can read the page tables
 * without mutating them (ie causing faults).
 */
int hmm_range_fault(struct hmm_range *range)
{
        struct hmm_vma_walk hmm_vma_walk = {
                .range = range,
                .last = range->start,
        };
        struct mm_struct *mm = range->notifier->mm;
        int ret;

        mmap_assert_locked(mm);

        do {
                /* If range is no longer valid force retry. */
                if (mmu_interval_check_retry(range->notifier,
                                             range->notifier_seq))
                        return -EBUSY;
                ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
                                      &hmm_walk_ops, &hmm_vma_walk);
                /*
                 * When -EBUSY is returned the loop restarts with
                 * hmm_vma_walk.last set to an address that has not been stored
                 * in pfns. All entries < last in the pfn array are set to their
                 * output, and all >= are still at their input values.
                 */
        } while (ret == -EBUSY);
        return ret;
}
EXPORT_SYMBOL(hmm_range_fault);