#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/swap.h>
#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/writeback.h>
#include <linux/mmu_notifier.h>
#include <linux/swapops.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>

#include "internal.h"

static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
		pte_t *pte, unsigned int flags)
{
	/* No page to get reference */
	if (flags & FOLL_GET)
		return -EFAULT;

	if (flags & FOLL_TOUCH) {
		pte_t entry = *pte;

		if (flags & FOLL_WRITE)
			entry = pte_mkdirty(entry);
		entry = pte_mkyoung(entry);

		if (!pte_same(*pte, entry)) {
			set_pte_at(vma->vm_mm, address, pte, entry);
			update_mmu_cache(vma, address, pte);
		}
	}

	/* Proper page table entry exists, but no corresponding struct page */
	return -EEXIST;
}

/*
 * FOLL_FORCE can write to even unwritable pte's, but only
 * after we've gone through a COW cycle and they are dirty.
 */
static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
{
	return pte_write(pte) ||
		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
}

/**
 * follow_page_mask - look up a page descriptor from a user-virtual address
 * @vma: vm_area_struct mapping @address
 * @address: virtual address to look up
 * @flags: flags modifying lookup behaviour
 * @page_mask: on output, *page_mask is set according to the size of the page
 *
 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 *
 * Returns the mapped (struct page *), %NULL if no mapping exists, or
 * an error pointer if there is a mapping to something not represented
 * by a page descriptor (see also vm_normal_page()).
 */
struct page *follow_page_mask(struct vm_area_struct *vma,
			      unsigned long address, unsigned int flags,
			      unsigned int *page_mask)
{
	struct dev_pagemap *pgmap = NULL;
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *ptep, pte;
	spinlock_t *ptl;
	struct page *page;
	struct mm_struct *mm = vma->vm_mm;

	*page_mask = 0;

	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
	if (!IS_ERR(page)) {
		/*
		 * RHEL: BZ1268999 quick-and-dirty-fix
		 *
		 * On powerpc a race between a THP pmd clear path and
		 * follow_huge_addr() can result in follow_huge_addr()
		 * returning NULL when a THP PMD has just been cleared
		 * - usually follow_huge_addr() should return
		 * ERR_PTR(-EINVAL) on a THP PMD.  This hack avoids
		 * the BUG_ON() while waiting for a proper upstream
		 * fix.  It will mean follow_page_mask() fails, but
		 * should trigger a fall back to a faultin path which
		 * should populate the pages.
		 */
		if (page)
			BUG_ON(flags & FOLL_GET);
		goto out;
	}

	page = NULL;
	pgd = pgd_offset(mm, address);
	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
		goto no_page_table;

	pud = pud_offset(pgd, address);
	if (pud_none(*pud))
		goto no_page_table;
	if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
		page = follow_huge_pud(mm, address, pud, flags);
		if (page)
			return page;
		goto no_page_table;
	}
	if (pud_devmap(*pud)) {
		ptl = pud_lock(mm, pud);
		page = follow_devmap_pud(vma, address, pud, flags);
		spin_unlock(ptl);
		if (page)
			return page;
	}
	if (unlikely(pud_bad(*pud)))
		goto no_page_table;

	pmd = pmd_offset(pud, address);
	if (pmd_none(*pmd))
		goto no_page_table;
	if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
		page = follow_huge_pmd(mm, address, pmd, flags);
		if (page)
			return page;
		goto no_page_table;
	}
	if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
		goto no_page_table;
	if (pmd_devmap(*pmd)) {
		ptl = pmd_lock(mm, pmd);
		page = follow_devmap_pmd(vma, address, pmd, flags);
		spin_unlock(ptl);
		if (page)
			return page;
	}
	if (pmd_trans_huge(*pmd)) {
		if (flags & FOLL_SPLIT) {
			split_huge_page_pmd(vma, address, pmd);
			goto split_fallthrough;
		}
		ptl = pmd_lock(mm, pmd);
		if (likely(pmd_trans_huge(*pmd))) {
			if (unlikely(pmd_trans_splitting(*pmd))) {
				spin_unlock(ptl);
				wait_split_huge_page(vma->anon_vma, pmd);
			} else {
				page = follow_trans_huge_pmd(vma, address,
							     pmd, flags);
				spin_unlock(ptl);
				*page_mask = HPAGE_PMD_NR - 1;
				goto out;
			}
		} else
			spin_unlock(ptl);
		/* fall through */
	}
split_fallthrough:
	if (unlikely(pmd_bad(*pmd)))
		goto no_page_table;

	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);

	pte = *ptep;
	if (!pte_present(pte)) {
		swp_entry_t entry;
		/*
		 * KSM's break_ksm() relies upon recognizing a ksm page
		 * even while it is being migrated, so for that case we
		 * need migration_entry_wait().
		 */
		if (likely(!(flags & FOLL_MIGRATION)))
			goto no_page;
		if (pte_none(pte) || pte_file(pte))
			goto no_page;
		entry = pte_to_swp_entry(pte);
		if (!is_migration_entry(entry))
			goto no_page;
		if (is_migration_entry(entry)) {
			pte_unmap_unlock(ptep, ptl);
			migration_entry_wait(mm, pmd, address);
			goto split_fallthrough;
		}
		goto no_page;
	}
	if ((flags & FOLL_NUMA) && pte_numa(pte))
		goto no_page;
	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
		goto unlock;

	page = vm_normal_page(vma, address, pte);
	if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
		/*
		 * Only return device mapping pages in the FOLL_GET case since
		 * they are only valid while holding the pgmap reference.
		 */
		pgmap = get_dev_pagemap(pte_pfn(pte), NULL);
		if (pgmap)
			page = pte_page(pte);
		else
			goto no_page;
	} else if (unlikely(!page)) {
		if (flags & FOLL_DUMP) {
			/* Avoid special (like zero) pages in core dumps */
			page = ERR_PTR(-EFAULT);
			goto unlock;
		}

		if (is_zero_pfn(pte_pfn(pte))) {
			page = pte_page(pte);
		} else {
			int ret;

			ret = follow_pfn_pte(vma, address, ptep, flags);
			page = ERR_PTR(ret);
			goto unlock;
		}
	}

	if (flags & FOLL_GET) {
		get_page_foll(page);

		/* drop the pgmap reference now that we hold the page */
		if (pgmap) {
			put_dev_pagemap(pgmap);
			pgmap = NULL;
		}
	}
	if (flags & FOLL_TOUCH) {
		if ((flags & FOLL_WRITE) &&
		    !pte_dirty(pte) && !PageDirty(page))
			set_page_dirty(page);
		/*
		 * pte_mkyoung() would be more correct here, but atomic care
		 * is needed to avoid losing the dirty bit: it is easier to use
		 * mark_page_accessed().
		 */
		mark_page_accessed(page);
	}
	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
		/*
		 * The preliminary mapping check is mainly to avoid the
		 * pointless overhead of lock_page on the ZERO_PAGE
		 * which might bounce very badly if there is contention.
		 *
		 * If the page is already locked, we don't need to
		 * handle it now - vmscan will handle it later if and
		 * when it attempts to reclaim the page.
		 */
		if (page->mapping && trylock_page(page)) {
			lru_add_drain();  /* push cached pages to LRU */
			/*
			 * Because we lock page here, and migration is
			 * blocked by the pte's page reference, and we
			 * know the page is still mapped, we don't even
			 * need to check for file-cache page truncation.
			 */
			mlock_vma_page(page);
			unlock_page(page);
		}
	}
unlock:
	pte_unmap_unlock(ptep, ptl);
out:
	return page;

no_page:
	pte_unmap_unlock(ptep, ptl);
	if (!pte_none(pte))
		return page;

no_page_table:
	/*
	 * When core dumping an enormous anonymous area that nobody
	 * has touched so far, we don't want to allocate unnecessary pages or
	 * page tables.  Return error instead of NULL to skip handle_mm_fault,
	 * then get_dump_page() will return NULL to leave a hole in the dump.
	 * But we can only make this optimization where a hole would surely
	 * be zero-filled if handle_mm_fault() actually did handle it.
	 */
	if ((flags & FOLL_DUMP) &&
	    (!vma->vm_ops || !vma->vm_ops->fault))
		return ERR_PTR(-EFAULT);
	return page;
}

/**
 * __get_user_pages() - pin user pages in memory
 * @tsk:	task_struct of target task
 * @mm:		mm_struct of target mm
 * @start:	starting user address
 * @nr_pages:	number of pages from start to pin
 * @gup_flags:	flags modifying pin behaviour
 * @pages:	array that receives pointers to the pages pinned.
 *		Should be at least nr_pages long. Or NULL, if caller
 *		only intends to ensure the pages are faulted in.
 * @vmas:	array of pointers to vmas corresponding to each page.
 *		Or NULL if the caller does not require them.
 * @nonblocking: whether waiting for disk IO or mmap_sem contention
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
 * Must be called with mmap_sem held for read or write.
 *
 * __get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * __get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
 * appropriate) must be called after the page is finished with, and
 * before put_page is called.
 *
 * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
 * or mmap_sem contention, and if waiting is needed to pin all pages,
 * *@nonblocking will be set to 0.
 *
 * In most cases, get_user_pages or get_user_pages_fast should be used
 * instead of __get_user_pages. __get_user_pages should be used only if
 * you need some special @gup_flags.
 */
long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
		unsigned long start, unsigned long nr_pages,
		unsigned int gup_flags, struct page **pages,
		struct vm_area_struct **vmas, int *nonblocking)
{
	long i;
	unsigned long vm_flags;
	unsigned int page_mask;
	int write = (gup_flags & FOLL_WRITE);
	int foreign = (gup_flags & FOLL_REMOTE);

	if (!nr_pages)
		return 0;

	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

	/* 
	 * Require read or write permissions.
	 * If FOLL_FORCE is set, we only require the "MAY" flags.
	 */
	vm_flags  = (gup_flags & FOLL_WRITE) ?
			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
	vm_flags &= (gup_flags & FOLL_FORCE) ?
			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);

	/*
	 * If FOLL_FORCE and FOLL_NUMA are both set, handle_mm_fault
	 * would be called on PROT_NONE ranges. We must never invoke
	 * handle_mm_fault on PROT_NONE ranges or the NUMA hinting
	 * page faults would unprotect the PROT_NONE ranges if
	 * _PAGE_NUMA and _PAGE_PROTNONE are sharing the same pte/pmd
	 * bitflag. So to avoid that, don't set FOLL_NUMA if
	 * FOLL_FORCE is set.
	 */
	if (!(gup_flags & FOLL_FORCE))
		gup_flags |= FOLL_NUMA;

	i = 0;

	do {
		struct vm_area_struct *vma;

		vma = find_extend_vma(mm, start);
		if (!vma && in_gate_area(mm, start)) {
			unsigned long pg = start & PAGE_MASK;
			pgd_t *pgd;
			pud_t *pud;
			pmd_t *pmd;
			pte_t *pte;

			/* user gate pages are read-only */
			if (gup_flags & FOLL_WRITE)
				return i ? : -EFAULT;
			if (pg > TASK_SIZE)
				pgd = pgd_offset_k(pg);
			else
				pgd = pgd_offset_gate(mm, pg);
			BUG_ON(pgd_none(*pgd));
			pud = pud_offset(pgd, pg);
			BUG_ON(pud_none(*pud));
			pmd = pmd_offset(pud, pg);
			if (pmd_none(*pmd))
				return i ? : -EFAULT;
			VM_BUG_ON(pmd_trans_huge(*pmd));
			pte = pte_offset_map(pmd, pg);
			if (pte_none(*pte)) {
				pte_unmap(pte);
				return i ? : -EFAULT;
			}
			vma = get_gate_vma(mm);
			if (pages) {
				struct page *page;

				page = vm_normal_page(vma, start, *pte);
				if (!page) {
					if (!(gup_flags & FOLL_DUMP) &&
					     is_zero_pfn(pte_pfn(*pte)))
						page = pte_page(*pte);
					else {
						pte_unmap(pte);
						return i ? : -EFAULT;
					}
				}
				pages[i] = page;
				get_page(page);
			}
			pte_unmap(pte);
			page_mask = 0;
			goto next_page;
		}

		if (!vma ||
		    (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
		    !(vm_flags & vma->vm_flags))
			return i ? : -EFAULT;

		/*
		 * gups are always data accesses, not instruction
		 * fetches, so execute=false here
		 */
		if (!arch_vma_access_permitted(vma, write, false, foreign))
			return i ? : -EFAULT;

		if (is_vm_hugetlb_page(vma)) {
			i = follow_hugetlb_page(mm, vma, pages, vmas,
					&start, &nr_pages, i,
					gup_flags, nonblocking);
			continue;
		}

		do {
			struct page *page;
			unsigned int foll_flags = gup_flags;
			unsigned int page_increm;

			/*
			 * If we have a pending SIGKILL, don't keep faulting
			 * pages and potentially allocating memory.
			 */
			if (unlikely(fatal_signal_pending(current)))
				return i ? i : -ERESTARTSYS;

			cond_resched();
			while (!(page = follow_page_mask(vma, start,
						foll_flags, &page_mask))) {
				int ret;
				unsigned int fault_flags = 0;

				if (foll_flags & FOLL_WRITE)
					fault_flags |= FAULT_FLAG_WRITE;
				if (foll_flags & FOLL_REMOTE)
					fault_flags |= FAULT_FLAG_REMOTE;
				if (nonblocking)
					fault_flags |= FAULT_FLAG_ALLOW_RETRY;
				if (foll_flags & FOLL_NOWAIT)
					fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);
				if (foll_flags & FOLL_TRIED) {
					WARN_ON_ONCE(fault_flags &
						     FAULT_FLAG_ALLOW_RETRY);
					fault_flags |= FAULT_FLAG_TRIED;
				}

				ret = handle_mm_fault(vma, start,
							fault_flags);

				if (ret & VM_FAULT_ERROR) {
					if (ret & VM_FAULT_OOM)
						return i ? i : -ENOMEM;
					if (ret & (VM_FAULT_HWPOISON |
						   VM_FAULT_HWPOISON_LARGE)) {
						if (i)
							return i;
						else if (gup_flags & FOLL_HWPOISON)
							return -EHWPOISON;
						else
							return -EFAULT;
					}
					if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
						return i ? i : -EFAULT;
					BUG();
				}

				if (tsk) {
					if (ret & VM_FAULT_MAJOR)
						tsk->maj_flt++;
					else
						tsk->min_flt++;
				}

				if (ret & VM_FAULT_RETRY) {
					if (nonblocking)
						*nonblocking = 0;
					return i;
				}

				/*
				 * The VM_FAULT_WRITE bit tells us that
				 * do_wp_page has broken COW when necessary,
				 * even if maybe_mkwrite decided not to set
				 * pte_write. We can thus safely do subsequent
				 * page lookups as if they were reads. But only
				 * do so when looping for pte_write is futile:
				 * in some cases userspace may also be wanting
				 * to write to the gotten user page, which a
				 * read fault here might prevent (a readonly
				 * page might get reCOWed by userspace write).
				 */
				if ((ret & VM_FAULT_WRITE) &&
				    !(vma->vm_flags & VM_WRITE))
					foll_flags |= FOLL_COW;

				cond_resched();
			}
			if (PTR_ERR(page) == -EEXIST) {
				/*
				 * Proper page table entry exists, but
				 * no corresponding struct page.
				 */
				goto next_page;
			} else if (IS_ERR(page)) {
				return i ? i : PTR_ERR(page);
			}
			if (pages) {
				pages[i] = page;

				flush_anon_page(vma, page, start);
				flush_dcache_page(page);
				page_mask = 0;
			}
next_page:
			if (vmas) {
				vmas[i] = vma;
				page_mask = 0;
			}
			page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
			if (page_increm > nr_pages)
				page_increm = nr_pages;
			i += page_increm;
			start += page_increm * PAGE_SIZE;
			nr_pages -= page_increm;
		} while (nr_pages && start < vma->vm_end);
	} while (nr_pages);
	return i;
}
EXPORT_SYMBOL(__get_user_pages);

bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
{
	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;

	if (!(vm_flags & vma->vm_flags))
		return false;

	/*
	 * The architecture might have a hardware protection
	 * mechanism other than read/write that can deny access.
	 *
	 * gup always represents data access, not instruction
	 * fetches, so execute=false here:
	 */
	if (!arch_vma_access_permitted(vma, write, false, foreign))
		return false;

	return true;
}

/*
 * fixup_user_fault() - manually resolve a user page fault
 * @tsk:	the task_struct to use for page fault accounting, or
 *		NULL if faults are not to be recorded.
 * @mm:		mm_struct of target mm
 * @address:	user address
 * @fault_flags:flags to pass down to handle_mm_fault()
 *
 * This is meant to be called in the specific scenario where for locking reasons
 * we try to access user memory in atomic context (within a pagefault_disable()
 * section), this returns -EFAULT, and we want to resolve the user fault before
 * trying again.
 *
 * Typically this is meant to be used by the futex code.
 *
 * The main difference with get_user_pages() is that this function will
 * unconditionally call handle_mm_fault() which will in turn perform all the
 * necessary SW fixup of the dirty and young bits in the PTE, while
 * handle_mm_fault() only guarantees to update these in the struct page.
 *
 * This is important for some architectures where those bits also gate the
 * access permission to the page because they are maintained in software.  On
 * such architectures, gup() will not be enough to make a subsequent access
 * succeed.
 *
 * This should be called with the mm_sem held for read.
 */
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
		     unsigned long address, unsigned int fault_flags)
{
	struct vm_area_struct *vma;
	int ret;

	vma = find_extend_vma(mm, address);
	if (!vma || address < vma->vm_start)
		return -EFAULT;

	if (!vma_permits_fault(vma, fault_flags))
		return -EFAULT;

	ret = handle_mm_fault(vma, address, fault_flags);
	if (ret & VM_FAULT_ERROR) {
		if (ret & VM_FAULT_OOM)
			return -ENOMEM;
		if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
			return -EHWPOISON;
		if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
			return -EFAULT;
		BUG();
	}
	if (tsk) {
		if (ret & VM_FAULT_MAJOR)
			tsk->maj_flt++;
		else
			tsk->min_flt++;
	}
	return 0;
}
EXPORT_SYMBOL_GPL(fixup_user_fault);

static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
						struct mm_struct *mm,
						unsigned long start,
						unsigned long nr_pages,
						int write, int force,
						struct page **pages,
						struct vm_area_struct **vmas,
						int *locked, bool notify_drop,
						unsigned int flags)
{
	long ret, pages_done;
	bool lock_dropped;

	if (locked) {
		/* if VM_FAULT_RETRY can be returned, vmas become invalid */
		BUG_ON(vmas);
		/* check caller initialized locked */
		BUG_ON(*locked != 1);
	}

	if (pages)
		flags |= FOLL_GET;
	if (write)
		flags |= FOLL_WRITE;
	if (force)
		flags |= FOLL_FORCE;

	pages_done = 0;
	lock_dropped = false;
	for (;;) {
		ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
				       vmas, locked);
		if (!locked)
			/* VM_FAULT_RETRY couldn't trigger, bypass */
			return ret;

		/* VM_FAULT_RETRY cannot return errors */
		if (!*locked) {
			BUG_ON(ret < 0);
			BUG_ON(ret >= nr_pages);
		}

		if (!pages)
			/* If it's a prefault don't insist harder */
			return ret;

		if (ret > 0) {
			nr_pages -= ret;
			pages_done += ret;
			if (!nr_pages)
				break;
		}
		if (*locked) {
			/* VM_FAULT_RETRY didn't trigger */
			if (!pages_done)
				pages_done = ret;
			break;
		}
		/* VM_FAULT_RETRY triggered, so seek to the faulting offset */
		pages += ret;
		start += ret << PAGE_SHIFT;

		/*
		 * Repeat on the address that fired VM_FAULT_RETRY
		 * without FAULT_FLAG_ALLOW_RETRY but with
		 * FAULT_FLAG_TRIED.
		 */
		*locked = 1;
		lock_dropped = true;
		down_read(&mm->mmap_sem);
		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
				       pages, NULL, NULL);
		if (ret != 1) {
			BUG_ON(ret > 1);
			if (!pages_done)
				pages_done = ret;
			break;
		}
		nr_pages--;
		pages_done++;
		if (!nr_pages)
			break;
		pages++;
		start += PAGE_SIZE;
	}
	if (notify_drop && lock_dropped && *locked) {
		/*
		 * We must let the caller know we temporarily dropped the lock
		 * and so the critical section protected by it was lost.
		 */
		up_read(&mm->mmap_sem);
		*locked = 0;
	}
	return pages_done;
}

/*
 * We can leverage the VM_FAULT_RETRY functionality in the page fault
 * paths better by using either get_user_pages_locked() or
 * get_user_pages_unlocked().
 *
 * get_user_pages_locked() is suitable to replace the form:
 *
 *      down_read(&mm->mmap_sem);
 *      do_something()
 *      get_user_pages(tsk, mm, ..., pages, NULL);
 *      up_read(&mm->mmap_sem);
 *
 *  to:
 *
 *      int locked = 1;
 *      down_read(&mm->mmap_sem);
 *      do_something()
 *      get_user_pages_locked(tsk, mm, ..., pages, &locked);
 *      if (locked)
 *          up_read(&mm->mmap_sem);
 */
long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm,
			   unsigned long start, unsigned long nr_pages,
			   int write, int force, struct page **pages,
			   int *locked)
{
	return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
				       pages, NULL, locked, true, FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages_locked);

/*
 * Same as get_user_pages_unlocked(...., FOLL_TOUCH) but it allows to
 * pass additional gup_flags as last parameter (like FOLL_HWPOISON).
 *
 * NOTE: here FOLL_TOUCH is not set implicitly and must be set by the
 * caller if required (just like with __get_user_pages). "FOLL_GET",
 * "FOLL_WRITE" and "FOLL_FORCE" are set implicitly as needed
 * according to the parameters "pages", "write", "force"
 * respectively.
 */
__always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
					       unsigned long start, unsigned long nr_pages,
					       int write, int force, struct page **pages,
					       unsigned int gup_flags)
{
	long ret;
	int locked = 1;
	down_read(&mm->mmap_sem);
	ret = __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
				      pages, NULL, &locked, false, gup_flags);
	if (locked)
		up_read(&mm->mmap_sem);
	return ret;
}
EXPORT_SYMBOL(__get_user_pages_unlocked);

/*
 * get_user_pages_unlocked() is suitable to replace the form:
 *
 *      down_read(&mm->mmap_sem);
 *      get_user_pages(tsk, mm, ..., pages, NULL);
 *      up_read(&mm->mmap_sem);
 *
 *  with:
 *
 *      get_user_pages_unlocked(tsk, mm, ..., pages);
 *
 * It is functionally equivalent to get_user_pages_fast so
 * get_user_pages_fast should be used instead, if the two parameters
 * "tsk" and "mm" are respectively equal to current and current->mm,
 * or if "force" shall be set to 1 (get_user_pages_fast misses the
 * "force" parameter).
 */
long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
			     unsigned long start, unsigned long nr_pages,
			     int write, int force, struct page **pages)
{
	return __get_user_pages_unlocked(tsk, mm, start, nr_pages, write,
					 force, pages, FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages_unlocked);

/*
 * get_user_pages_remote() - pin user pages in memory
 * @tsk:	the task_struct to use for page fault accounting, or
 *		NULL if faults are not to be recorded.
 * @mm:		mm_struct of target mm
 * @start:	starting user address
 * @nr_pages:	number of pages from start to pin
 * @write:	whether pages will be written to by the caller
 * @force:	whether to force write access even if user mapping is
 *		readonly. This will result in the page being COWed even
 *		in MAP_SHARED mappings. You do not want this.
 * @pages:	array that receives pointers to the pages pinned.
 *		Should be at least nr_pages long. Or NULL, if caller
 *		only intends to ensure the pages are faulted in.
 * @vmas:	array of pointers to vmas corresponding to each page.
 *		Or NULL if the caller does not require them.
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
 * Must be called with mmap_sem held for read or write.
 *
 * get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
 * If write=0, the page must not be written to. If the page is written to,
 * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
 * after the page is finished with, and before put_page is called.
 *
 * get_user_pages is typically used for fewer-copy IO operations, to get a
 * handle on the memory by some means other than accesses via the user virtual
 * addresses. The pages may be submitted for DMA to devices or accessed via
 * their kernel linear mapping (via the kmap APIs). Care should be taken to
 * use the correct cache flushing APIs.
 *
 * See also get_user_pages_fast, for performance critical applications.
 *
 * get_user_pages should be phased out in favor of
 * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
 * should use get_user_pages because it cannot pass
 * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
 */
long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
		unsigned long start, unsigned long nr_pages,
		int write, int force, struct page **pages,
		struct vm_area_struct **vmas)
{
	return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
				       pages, vmas, NULL, false,
				       FOLL_TOUCH | FOLL_REMOTE);
}
EXPORT_SYMBOL(get_user_pages_remote);

/*
 * This is the same as get_user_pages_remote() for the time
 * being.
 */
long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
		unsigned long start, unsigned long nr_pages,
		int write, int force, struct page **pages,
		struct vm_area_struct **vmas)
{
	return __get_user_pages_locked(tsk, mm, start, nr_pages,
				       write, force, pages, vmas, NULL, false,
				       FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages);

/**
 * get_dump_page() - pin user page in memory while writing it to core dump
 * @addr: user address
 *
 * Returns struct page pointer of user page pinned for dump,
 * to be freed afterwards by page_cache_release() or put_page().
 *
 * Returns NULL on any kind of failure - a hole must then be inserted into
 * the corefile, to preserve alignment with its headers; and also returns
 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
 * allowing a hole to be left in the corefile to save diskspace.
 *
 * Called without mmap_sem, but after all other threads have been killed.
 */
#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
	struct vm_area_struct *vma;
	struct page *page;

	if (__get_user_pages(current, current->mm, addr, 1,
			     FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
			     NULL) < 1)
		return NULL;
	flush_cache_page(vma, addr, page_to_pfn(page));
	return page;
}
#endif /* CONFIG_ELF_CORE */