// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * Copyright 2013 Red Hat Inc.
   *

   * 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, NULL) &
  		    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);