linux/mm/hmm.c

// 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/hmm-dma.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/oom.h>
#include <linux/pagemap.h>
#include <linux/leafops.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/pci-p2pdma.h>
#include <linux/mmu_notifier.h>
#include <linux/memory_hotplug.h>

#include "internal.h"

struct hmm_vma_walk {
	struct hmm_range	*range;
	bool			*locked;
	unsigned long		last;
	unsigned long		end;
	unsigned int		required_fault;
};

/*
 * Internal sentinel returned by walk callbacks when they need a page fault.
 * The callback stores end/required_fault in hmm_vma_walk; the outer loop
 * consumes the sentinel and never propagates it to the caller.
 */
#define HMM_FAULT_PENDING	-EAGAIN

/*
 * Internal sentinel returned by hmm_do_fault() when handle_mm_fault()
 * completes a page fault with the mmap lock dropped. hmm_do_fault() sets
 * *locked = false; the outer loop consumes the sentinel and never propagates
 * it to the caller.
 */
#define HMM_FAULT_UNLOCKED	-ENOLCK

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

enum {
	/* These flags are carried from input-to-output */
	HMM_PFN_INOUT_FLAGS = HMM_PFN_DMA_MAPPED | HMM_PFN_P2PDMA |
			      HMM_PFN_P2PDMA_BUS,
};

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] &= HMM_PFN_INOUT_FLAGS;
		range->hmm_pfns[i] |= cpu_flags;
	}
	return 0;
}

/*
 * hmm_record_fault() - record a range that needs to be faulted in
 *
 * Called by the walk callbacks when they discover that part of the range
 * needs a page fault.  The callback records what to fault and returns
 * HMM_FAULT_PENDING; the outer loop in hmm_range_fault_locked() drops
 * back out of walk_page_range() and invokes handle_mm_fault() from a context
 * where no page-table or hugetlb_vma_lock is held.
 */
static int hmm_record_fault(unsigned long addr, unsigned long end,
			    unsigned int required_fault,
			    struct mm_walk *walk)
{
	struct hmm_vma_walk *hmm_vma_walk = walk->private;

	WARN_ON_ONCE(!required_fault);
	hmm_vma_walk->last = addr;
	hmm_vma_walk->end = end;
	hmm_vma_walk->required_fault = required_fault;
	return HMM_FAULT_PENDING;
}

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_record_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;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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);
}

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_record_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] &= HMM_PFN_INOUT_FLAGS;
		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 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_get(ptep);
	uint64_t pfn_req_flags = *hmm_pfn;
	uint64_t new_pfn_flags = 0;

	/*
	 * Any other marker than a UFFD WP marker will result in a fault error
	 * that will be correctly handled, so we need only check for UFFD WP
	 * here.
	 */
	if (pte_none(pte) || pte_is_uffd_wp_marker(pte)) {
		required_fault =
			hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
		if (required_fault)
			goto fault;
		goto out;
	}

	if (!pte_present(pte)) {
		const softleaf_t entry = softleaf_from_pte(pte);

		/*
		 * Don't fault in device private pages owned by the caller,
		 * just report the PFN.
		 */
		if (softleaf_is_device_private(entry) &&
		    page_pgmap(softleaf_to_page(entry))->owner ==
		    range->dev_private_owner) {
			cpu_flags = HMM_PFN_VALID;
			if (softleaf_is_device_private_write(entry))
				cpu_flags |= HMM_PFN_WRITE;
			new_pfn_flags = softleaf_to_pfn(entry) | cpu_flags;
			goto out;
		}

		required_fault =
			hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
		if (!required_fault)
			goto out;

		if (softleaf_is_swap(entry))
			goto fault;

		if (softleaf_is_device_private(entry))
			goto fault;

		if (softleaf_is_device_exclusive(entry))
			goto fault;

		if (softleaf_is_migration(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 (!vm_normal_page(walk->vma, addr, pte) &&
	    !is_zero_pfn(pte_pfn(pte))) {
		if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
			pte_unmap(ptep);
			return -EFAULT;
		}
		new_pfn_flags = HMM_PFN_ERROR;
		goto out;
	}

	new_pfn_flags = pte_pfn(pte) | cpu_flags;
out:
	*hmm_pfn = (*hmm_pfn & HMM_PFN_INOUT_FLAGS) | new_pfn_flags;
	return 0;

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

#ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
static int hmm_vma_handle_absent_pmd(struct mm_walk *walk, unsigned long start,
				     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 npages = (end - start) >> PAGE_SHIFT;
	const softleaf_t entry = softleaf_from_pmd(pmd);
	unsigned long addr = start;
	unsigned int required_fault;

	if (softleaf_is_device_private(entry) &&
	    softleaf_to_folio(entry)->pgmap->owner ==
	    range->dev_private_owner) {
		unsigned long cpu_flags = HMM_PFN_VALID |
			hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
		unsigned long pfn = softleaf_to_pfn(entry);
		unsigned long i;

		if (softleaf_is_device_private_write(entry))
			cpu_flags |= HMM_PFN_WRITE;

		/*
		 * Fully populate the PFN list though subsequent PFNs could be
		 * inferred, because drivers which are not yet aware of large
		 * folios probably do not support sparsely populated PFN lists.
		 */
		for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
			hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
			hmm_pfns[i] |= pfn | cpu_flags;
		}

		return 0;
	}

	required_fault = hmm_range_need_fault(hmm_vma_walk, hmm_pfns,
					      npages, 0);
	if (required_fault) {
		if (softleaf_is_device_private(entry))
			return hmm_record_fault(addr, end, required_fault, walk);
		else
			return -EFAULT;
	}

	return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
}
#else
static int hmm_vma_handle_absent_pmd(struct mm_walk *walk, unsigned long start,
				     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 npages = (end - start) >> PAGE_SHIFT;

	if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0))
		return -EFAULT;
	return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
}
#endif  /* CONFIG_ARCH_HAS_PMD_SOFTLEAVES */

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 = pmdp_get_lockless(pmdp);
	if (pmd_none(pmd))
		return hmm_vma_walk_hole(start, end, -1, walk);

	if (thp_migration_supported() && pmd_is_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))
		return hmm_vma_handle_absent_pmd(walk, start, end, hmm_pfns,
						 pmd);

	if (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 = pmdp_get_lockless(pmdp);
		if (!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);
	if (!ptep)
		goto again;
	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_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;
	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 = pudp_get(pudp);
	if (!pud_present(pud)) {
		spin_unlock(ptl);
		return hmm_vma_walk_hole(start, end, -1, walk);
	}

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

		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_record_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] &= HMM_PFN_INOUT_FLAGS;
			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 0;
}
#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(walk->mm, addr, 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_record_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] &= HMM_PFN_INOUT_FLAGS;
		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)) &&
	    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,
	.walk_lock	= PGWALK_RDLOCK,
};

/*
 * hmm_do_fault - fault in a range recorded by a walk callback
 *
 * Called from the outer loop in hmm_range_fault_locked() after a callback
 * returned HMM_FAULT_PENDING.  At this point we hold only mmap_lock;
 * the page-table spinlock and any hugetlb_vma_lock acquired by the walk
 * framework have already been released by the unwind.
 *
 * Returns -EBUSY on success (all pages faulted, caller should re-walk).
 * Returns a negative errno on failure.
 */
static int hmm_do_fault(struct mm_struct *mm,
			struct hmm_vma_walk *hmm_vma_walk)
{
	unsigned long addr = hmm_vma_walk->last;
	unsigned long end = hmm_vma_walk->end;
	unsigned int required_fault = hmm_vma_walk->required_fault;
	unsigned int fault_flags = FAULT_FLAG_REMOTE;
	struct vm_area_struct *vma;

	if (hmm_vma_walk->locked)
		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

	vma = vma_lookup(mm, addr);
	if (!vma)
		return -EFAULT;

	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) {
		vm_fault_t ret;

		ret = handle_mm_fault(vma, addr, fault_flags, NULL);

		if (ret & (VM_FAULT_COMPLETED | VM_FAULT_RETRY)) {
			if (hmm_vma_walk->locked)    /* needed by sparse */
				*hmm_vma_walk->locked = false;
			else
				WARN_ON_ONCE(1);    /* broken fault handler */
			return HMM_FAULT_UNLOCKED;
		}

		if (ret & VM_FAULT_ERROR) {
			int err = vm_fault_to_errno(ret, 0);

			if (WARN_ON(!err))
				err = -EINVAL;

			return err;
		}
	}

	return -EBUSY;
}

static int hmm_range_fault_locked(struct hmm_range *range, bool *locked)
{
	struct hmm_vma_walk hmm_vma_walk = {
		.range = range,
		.locked = locked,
		.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 HMM_FAULT_PENDING is returned a walk callback
		 * recorded a range that needs handle_mm_fault();
		 * hmm_do_fault() runs the fault outside walk_page_range()
		 * (so no page-table or hugetlb_vma_lock is held) and
		 * returns -EBUSY so the loop re-walks and picks up the
		 * now-present entries.
		 */
		if (ret == HMM_FAULT_PENDING) {
			ret = hmm_do_fault(mm, &hmm_vma_walk);
			if (ret == HMM_FAULT_UNLOCKED) {
				if (fatal_signal_pending(current))
					return -EINTR;
				return -EBUSY;
			}
		}
		/*
		 * 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;
}

/**
 * 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).
 *
 * The mmap lock must be held by the caller and will remain held on return.
 * New users should prefer hmm_range_fault_unlocked_timeout() unless they
 * specifically need to keep the mmap lock held across the call. This helper
 * cannot support VMAs whose fault handlers need to drop the mmap lock.
 */
int hmm_range_fault(struct hmm_range *range)
{
	return hmm_range_fault_locked(range, NULL);
}
EXPORT_SYMBOL(hmm_range_fault);

/**
 * hmm_range_fault_unlocked_timeout - fault in a range with a retry timeout
 * @range:	argument structure
 * @timeout:	timeout in jiffies for internal -EBUSY retries, or 0 to retry
 *		indefinitely
 *
 * The caller must not hold the mmap lock. The function takes the mmap read
 * lock internally and allows handle_mm_fault() to drop it during faults. If
 * the mmap lock is dropped or the range is invalidated, the function refreshes
 * range->notifier_seq and restarts the walk internally.
 *
 * Passing 0 for @timeout retries indefinitely. A non-zero @timeout is a caller
 * policy limit for repeated mmu-notifier invalidation retries. HMM does not
 * interrupt page fault handling when the timeout expires, but returns -EBUSY
 * if the retry budget is exhausted before a stable range is obtained.
 *
 * Returns 0 on success or one of the error codes documented for
 * hmm_range_fault(). -EINTR is returned if mmap_lock acquisition is
 * interrupted or a fatal signal is pending during retry handling.
 */
int hmm_range_fault_unlocked_timeout(struct hmm_range *range,
				     unsigned long timeout)
{
	struct mm_struct *mm = range->notifier->mm;
	unsigned long deadline = 0;
	bool locked = false;
	int ret;

	do {
		/*
		 * If the previous fault dropped mmap_lock, then the fault
		 * handler made progress. Restart the retry timeout in that
		 * case, but keep the existing deadline for ordinary -EBUSY
		 * retries.
		 */
		if (timeout && !locked)
			deadline = jiffies + timeout;

		range->notifier_seq =
			mmu_interval_read_begin(range->notifier);

		ret = mmap_read_lock_killable(mm);
		if (ret)
			return ret;

		if (check_stable_address_space(mm)) {
			mmap_read_unlock(mm);
			return -EFAULT;
		}

		if (timeout && time_after(jiffies, deadline)) {
			mmap_read_unlock(mm);
			return -EBUSY;
		}

		locked = true;
		ret = hmm_range_fault_locked(range, &locked);
		if (locked)
			mmap_read_unlock(mm);
	} while (ret == -EBUSY);

	return ret;
}
EXPORT_SYMBOL(hmm_range_fault_unlocked_timeout);

/**
 * hmm_dma_map_alloc - Allocate HMM map structure
 * @dev: device to allocate structure for
 * @map: HMM map to allocate
 * @nr_entries: number of entries in the map
 * @dma_entry_size: size of the DMA entry in the map
 *
 * Allocate the HMM map structure and all the lists it contains.
 * Return 0 on success, -ENOMEM on failure.
 */
int hmm_dma_map_alloc(struct device *dev, struct hmm_dma_map *map,
		      size_t nr_entries, size_t dma_entry_size)
{
	bool dma_need_sync = false;
	bool use_iova;

	WARN_ON_ONCE(!(nr_entries * PAGE_SIZE / dma_entry_size));

	/*
	 * The HMM API violates our normal DMA buffer ownership rules and can't
	 * transfer buffer ownership.  The dma_addressing_limited() check is a
	 * best approximation to ensure no swiotlb buffering happens.
	 */
#ifdef CONFIG_DMA_NEED_SYNC
	dma_need_sync = !dev_dma_skip_sync(dev);
#endif /* CONFIG_DMA_NEED_SYNC */
	if (dma_need_sync || dma_addressing_limited(dev))
		return -EOPNOTSUPP;

	map->dma_entry_size = dma_entry_size;
	map->pfn_list = kvcalloc(nr_entries, sizeof(*map->pfn_list),
				 GFP_KERNEL | __GFP_NOWARN);
	if (!map->pfn_list)
		return -ENOMEM;

	use_iova = dma_iova_try_alloc(dev, &map->state, 0,
			nr_entries * PAGE_SIZE);
	if (!use_iova && dma_need_unmap(dev)) {
		map->dma_list = kvzalloc_objs(*map->dma_list, nr_entries,
					      GFP_KERNEL | __GFP_NOWARN);
		if (!map->dma_list)
			goto err_dma;
	}
	return 0;

err_dma:
	kvfree(map->pfn_list);
	return -ENOMEM;
}
EXPORT_SYMBOL_GPL(hmm_dma_map_alloc);

/**
 * hmm_dma_map_free - iFree HMM map structure
 * @dev: device to free structure from
 * @map: HMM map containing the various lists and state
 *
 * Free the HMM map structure and all the lists it contains.
 */
void hmm_dma_map_free(struct device *dev, struct hmm_dma_map *map)
{
	if (dma_use_iova(&map->state))
		dma_iova_free(dev, &map->state);
	kvfree(map->pfn_list);
	kvfree(map->dma_list);
}
EXPORT_SYMBOL_GPL(hmm_dma_map_free);

/**
 * hmm_dma_map_pfn - Map a physical HMM page to DMA address
 * @dev: Device to map the page for
 * @map: HMM map
 * @idx: Index into the PFN and dma address arrays
 * @p2pdma_state: PCI P2P state.
 *
 * dma_alloc_iova() allocates IOVA based on the size specified by their use in
 * iova->size. Call this function after IOVA allocation to link whole @page
 * to get the DMA address. Note that very first call to this function
 * will have @offset set to 0 in the IOVA space allocated from
 * dma_alloc_iova(). For subsequent calls to this function on same @iova,
 * @offset needs to be advanced by the caller with the size of previous
 * page that was linked + DMA address returned for the previous page that was
 * linked by this function.
 */
dma_addr_t hmm_dma_map_pfn(struct device *dev, struct hmm_dma_map *map,
			   size_t idx,
			   struct pci_p2pdma_map_state *p2pdma_state)
{
	struct dma_iova_state *state = &map->state;
	dma_addr_t *dma_addrs = map->dma_list;
	unsigned long *pfns = map->pfn_list;
	struct page *page = hmm_pfn_to_page(pfns[idx]);
	phys_addr_t paddr = hmm_pfn_to_phys(pfns[idx]);
	size_t offset = idx * map->dma_entry_size;
	unsigned long attrs = DMA_ATTR_REQUIRE_COHERENT;
	dma_addr_t dma_addr;
	int ret;

	if ((pfns[idx] & HMM_PFN_DMA_MAPPED) &&
	    !(pfns[idx] & HMM_PFN_P2PDMA_BUS)) {
		/*
		 * We are in this flow when there is a need to resync flags,
		 * for example when page was already linked in prefetch call
		 * with READ flag and now we need to add WRITE flag
		 *
		 * This page was already programmed to HW and we don't want/need
		 * to unlink and link it again just to resync flags.
		 */
		if (dma_use_iova(state))
			return state->addr + offset;

		/*
		 * Without dma_need_unmap, the dma_addrs array is NULL, thus we
		 * need to regenerate the address below even if there already
		 * was a mapping. But !dma_need_unmap implies that the
		 * mapping stateless, so this is fine.
		 */
		if (dma_need_unmap(dev))
			return dma_addrs[idx];

		/* Continue to remapping */
	}

	switch (pci_p2pdma_state(p2pdma_state, dev, page)) {
	case PCI_P2PDMA_MAP_NONE:
		break;
	case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
		attrs |= DMA_ATTR_MMIO;
		pfns[idx] |= HMM_PFN_P2PDMA;
		break;
	case PCI_P2PDMA_MAP_BUS_ADDR:
		pfns[idx] |= HMM_PFN_P2PDMA_BUS | HMM_PFN_DMA_MAPPED;
		return pci_p2pdma_bus_addr_map(p2pdma_state->mem, paddr);
	default:
		return DMA_MAPPING_ERROR;
	}

	if (dma_use_iova(state)) {
		ret = dma_iova_link(dev, state, paddr, offset,
				    map->dma_entry_size, DMA_BIDIRECTIONAL,
				    attrs);
		if (ret)
			goto error;

		ret = dma_iova_sync(dev, state, offset, map->dma_entry_size);
		if (ret) {
			dma_iova_unlink(dev, state, offset, map->dma_entry_size,
					DMA_BIDIRECTIONAL, attrs);
			goto error;
		}

		dma_addr = state->addr + offset;
	} else {
		if (WARN_ON_ONCE(dma_need_unmap(dev) && !dma_addrs))
			goto error;

		dma_addr = dma_map_phys(dev, paddr, map->dma_entry_size,
					DMA_BIDIRECTIONAL, attrs);
		if (dma_mapping_error(dev, dma_addr))
			goto error;

		if (dma_need_unmap(dev))
			dma_addrs[idx] = dma_addr;
	}
	pfns[idx] |= HMM_PFN_DMA_MAPPED;
	return dma_addr;
error:
	pfns[idx] &= ~HMM_PFN_P2PDMA;
	return DMA_MAPPING_ERROR;

}
EXPORT_SYMBOL_GPL(hmm_dma_map_pfn);

/**
 * hmm_dma_unmap_pfn - Unmap a physical HMM page from DMA address
 * @dev: Device to unmap the page from
 * @map: HMM map
 * @idx: Index of the PFN to unmap
 *
 * Returns true if the PFN was mapped and has been unmapped, false otherwise.
 */
bool hmm_dma_unmap_pfn(struct device *dev, struct hmm_dma_map *map, size_t idx)
{
	const unsigned long valid_dma = HMM_PFN_VALID | HMM_PFN_DMA_MAPPED;
	struct dma_iova_state *state = &map->state;
	dma_addr_t *dma_addrs = map->dma_list;
	unsigned long *pfns = map->pfn_list;
	unsigned long attrs = DMA_ATTR_REQUIRE_COHERENT;

	if ((pfns[idx] & valid_dma) != valid_dma)
		return false;

	if (pfns[idx] & HMM_PFN_P2PDMA)
		attrs |= DMA_ATTR_MMIO;

	if (pfns[idx] & HMM_PFN_P2PDMA_BUS)
		; /* no need to unmap bus address P2P mappings */
	else if (dma_use_iova(state))
		dma_iova_unlink(dev, state, idx * map->dma_entry_size,
				map->dma_entry_size, DMA_BIDIRECTIONAL, attrs);
	else if (dma_need_unmap(dev))
		dma_unmap_phys(dev, dma_addrs[idx], map->dma_entry_size,
			       DMA_BIDIRECTIONAL, attrs);

	pfns[idx] &=
		~(HMM_PFN_DMA_MAPPED | HMM_PFN_P2PDMA | HMM_PFN_P2PDMA_BUS);
	return true;
}
EXPORT_SYMBOL_GPL(hmm_dma_unmap_pfn);