Merge tag 'mm-stable-2022-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton:
 "Almost all of MM here. A few things are still getting finished off,
  reviewed, etc.

   - Yang Shi has improved the behaviour of khugepaged collapsing of
     readonly file-backed transparent hugepages.

   - Johannes Weiner has arranged for zswap memory use to be tracked and
     managed on a per-cgroup basis.

   - Munchun Song adds a /proc knob ("hugetlb_optimize_vmemmap") for
     runtime enablement of the recent huge page vmemmap optimization
     feature.

   - Baolin Wang contributes a series to fix some issues around hugetlb
     pagetable invalidation.

   - Zhenwei Pi has fixed some interactions between hwpoisoned pages and
     virtualization.

   - Tong Tiangen has enabled the use of the presently x86-only
     page_table_check debugging feature on arm64 and riscv.

   - David Vernet has done some fixup work on the memcg selftests.

   - Peter Xu has taught userfaultfd to handle write protection faults
     against shmem- and hugetlbfs-backed files.

   - More DAMON development from SeongJae Park - adding online tuning of
     the feature and support for monitoring of fixed virtual address
     ranges. Also easier discovery of which monitoring operations are
     available.

   - Nadav Amit has done some optimization of TLB flushing during
     mprotect().

   - Neil Brown continues to labor away at improving our swap-over-NFS
     support.

   - David Hildenbrand has some fixes to anon page COWing versus
     get_user_pages().

   - Peng Liu fixed some errors in the core hugetlb code.

   - Joao Martins has reduced the amount of memory consumed by
     device-dax's compound devmaps.

   - Some cleanups of the arch-specific pagemap code from Anshuman
     Khandual.

   - Muchun Song has found and fixed some errors in the TLB flushing of
     transparent hugepages.

   - Roman Gushchin has done more work on the memcg selftests.

  ... and, of course, many smaller fixes and cleanups. Notably, the
  customary million cleanup serieses from Miaohe Lin"

* tag 'mm-stable-2022-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (381 commits)
  mm: kfence: use PAGE_ALIGNED helper
  selftests: vm: add the "settings" file with timeout variable
  selftests: vm: add "test_hmm.sh" to TEST_FILES
  selftests: vm: check numa_available() before operating "merge_across_nodes" in ksm_tests
  selftests: vm: add migration to the .gitignore
  selftests/vm/pkeys: fix typo in comment
  ksm: fix typo in comment
  selftests: vm: add process_mrelease tests
  Revert "mm/vmscan: never demote for memcg reclaim"
  mm/kfence: print disabling or re-enabling message
  include/trace/events/percpu.h: cleanup for "percpu: improve percpu_alloc_percpu event trace"
  include/trace/events/mmflags.h: cleanup for "tracing: incorrect gfp_t conversion"
  mm: fix a potential infinite loop in start_isolate_page_range()
  MAINTAINERS: add Muchun as co-maintainer for HugeTLB
  zram: fix Kconfig dependency warning
  mm/shmem: fix shmem folio swapoff hang
  cgroup: fix an error handling path in alloc_pagecache_max_30M()
  mm: damon: use HPAGE_PMD_SIZE
  tracing: incorrect isolate_mote_t cast in mm_vmscan_lru_isolate
  nodemask.h: fix compilation error with GCC12
  ...

1 files changed, 403 insertions, 170 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 2a12028a3749..54bcd5327b74 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -86,6 +86,7 @@
 
 #include "pgalloc-track.h"
 #include "internal.h"
+#include "swap.h"
 
 #if defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) && !defined(CONFIG_COMPILE_TEST)
 #warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
@@ -99,6 +100,8 @@ struct page *mem_map;
 EXPORT_SYMBOL(mem_map);
 #endif
 
+static vm_fault_t do_fault(struct vm_fault *vmf);
+
 /*
  * A number of key systems in x86 including ioremap() rely on the assumption
  * that high_memory defines the upper bound on direct map memory, then end
@@ -720,12 +723,14 @@ static void restore_exclusive_pte(struct vm_area_struct *vma,
 	else if (is_writable_device_exclusive_entry(entry))
 		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
 
+	VM_BUG_ON(pte_write(pte) && !(PageAnon(page) && PageAnonExclusive(page)));
+
 	/*
 	 * No need to take a page reference as one was already
 	 * created when the swap entry was made.
 	 */
 	if (PageAnon(page))
-		page_add_anon_rmap(page, vma, address, false);
+		page_add_anon_rmap(page, vma, address, RMAP_NONE);
 	else
 		/*
 		 * Currently device exclusive access only supports anonymous
@@ -790,17 +795,23 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 						&src_mm->mmlist);
 			spin_unlock(&mmlist_lock);
 		}
+		/* Mark the swap entry as shared. */
+		if (pte_swp_exclusive(*src_pte)) {
+			pte = pte_swp_clear_exclusive(*src_pte);
+			set_pte_at(src_mm, addr, src_pte, pte);
+		}
 		rss[MM_SWAPENTS]++;
 	} else if (is_migration_entry(entry)) {
 		page = pfn_swap_entry_to_page(entry);
 
 		rss[mm_counter(page)]++;
 
-		if (is_writable_migration_entry(entry) &&
+		if (!is_readable_migration_entry(entry) &&
 				is_cow_mapping(vm_flags)) {
 			/*
-			 * COW mappings require pages in both
-			 * parent and child to be set to read.
+			 * COW mappings require pages in both parent and child
+			 * to be set to read. A previously exclusive entry is
+			 * now shared.
 			 */
 			entry = make_readable_migration_entry(
 							swp_offset(entry));
@@ -825,7 +836,8 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		 */
 		get_page(page);
 		rss[mm_counter(page)]++;
-		page_dup_rmap(page, false);
+		/* Cannot fail as these pages cannot get pinned. */
+		BUG_ON(page_try_dup_anon_rmap(page, false, src_vma));
 
 		/*
 		 * We do not preserve soft-dirty information, because so
@@ -854,6 +866,14 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		if (try_restore_exclusive_pte(src_pte, src_vma, addr))
 			return -EBUSY;
 		return -ENOENT;
+	} else if (is_pte_marker_entry(entry)) {
+		/*
+		 * We're copying the pgtable should only because dst_vma has
+		 * uffd-wp enabled, do sanity check.
+		 */
+		WARN_ON_ONCE(!userfaultfd_wp(dst_vma));
+		set_pte_at(dst_mm, addr, dst_pte, pte);
+		return 0;
 	}
 	if (!userfaultfd_wp(dst_vma))
 		pte = pte_swp_clear_uffd_wp(pte);
@@ -862,19 +882,11 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 }
 
 /*
- * Copy a present and normal page if necessary.
+ * Copy a present and normal page.
  *
- * NOTE! The usual case is that this doesn't need to do
- * anything, and can just return a positive value. That
- * will let the caller know that it can just increase
- * the page refcount and re-use the pte the traditional
- * way.
- *
- * But _if_ we need to copy it because it needs to be
- * pinned in the parent (and the child should get its own
- * copy rather than just a reference to the same page),
- * we'll do that here and return zero to let the caller
- * know we're done.
+ * NOTE! The usual case is that this isn't required;
+ * instead, the caller can just increase the page refcount
+ * and re-use the pte the traditional way.
  *
  * And if we need a pre-allocated page but don't yet have
  * one, return a negative error to let the preallocation
@@ -884,25 +896,10 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 static inline int
 copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 		  pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
-		  struct page **prealloc, pte_t pte, struct page *page)
+		  struct page **prealloc, struct page *page)
 {
 	struct page *new_page;
-
-	/*
-	 * What we want to do is to check whether this page may
-	 * have been pinned by the parent process.  If so,
-	 * instead of wrprotect the pte on both sides, we copy
-	 * the page immediately so that we'll always guarantee
-	 * the pinned page won't be randomly replaced in the
-	 * future.
-	 *
-	 * The page pinning checks are just "has this mm ever
-	 * seen pinning", along with the (inexact) check of
-	 * the page count. That might give false positives for
-	 * for pinning, but it will work correctly.
-	 */
-	if (likely(!page_needs_cow_for_dma(src_vma, page)))
-		return 1;
+	pte_t pte;
 
 	new_page = *prealloc;
 	if (!new_page)
@@ -915,7 +912,7 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
 	*prealloc = NULL;
 	copy_user_highpage(new_page, page, addr, src_vma);
 	__SetPageUptodate(new_page);
-	page_add_new_anon_rmap(new_page, dst_vma, addr, false);
+	page_add_new_anon_rmap(new_page, dst_vma, addr);
 	lru_cache_add_inactive_or_unevictable(new_page, dst_vma);
 	rss[mm_counter(new_page)]++;
 
@@ -944,16 +941,24 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 	struct page *page;
 
 	page = vm_normal_page(src_vma, addr, pte);
-	if (page) {
-		int retval;
-
-		retval = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
-					   addr, rss, prealloc, pte, page);
-		if (retval <= 0)
-			return retval;
-
+	if (page && PageAnon(page)) {
+		/*
+		 * If this page may have been pinned by the parent process,
+		 * copy the page immediately for the child so that we'll always
+		 * guarantee the pinned page won't be randomly replaced in the
+		 * future.
+		 */
 		get_page(page);
-		page_dup_rmap(page, false);
+		if (unlikely(page_try_dup_anon_rmap(page, false, src_vma))) {
+			/* Page maybe pinned, we have to copy. */
+			put_page(page);
+			return copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
+						 addr, rss, prealloc, page);
+		}
+		rss[mm_counter(page)]++;
+	} else if (page) {
+		get_page(page);
+		page_dup_file_rmap(page, false);
 		rss[mm_counter(page)]++;
 	}
 
@@ -965,6 +970,7 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 		ptep_set_wrprotect(src_mm, addr, src_pte);
 		pte = pte_wrprotect(pte);
 	}
+	VM_BUG_ON(page && PageAnon(page) && PageAnonExclusive(page));
 
 	/*
 	 * If it's a shared mapping, mark it clean in
@@ -1222,6 +1228,38 @@ copy_p4d_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
 	return 0;
 }
 
+/*
+ * Return true if the vma needs to copy the pgtable during this fork().  Return
+ * false when we can speed up fork() by allowing lazy page faults later until
+ * when the child accesses the memory range.
+ */
+static bool
+vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
+{
+	/*
+	 * Always copy pgtables when dst_vma has uffd-wp enabled even if it's
+	 * file-backed (e.g. shmem). Because when uffd-wp is enabled, pgtable
+	 * contains uffd-wp protection information, that's something we can't
+	 * retrieve from page cache, and skip copying will lose those info.
+	 */
+	if (userfaultfd_wp(dst_vma))
+		return true;
+
+	if (src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP))
+		return true;
+
+	if (src_vma->anon_vma)
+		return true;
+
+	/*
+	 * Don't copy ptes where a page fault will fill them correctly.  Fork
+	 * becomes much lighter when there are big shared or private readonly
+	 * mappings. The tradeoff is that copy_page_range is more efficient
+	 * than faulting.
+	 */
+	return false;
+}
+
 int
 copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 {
@@ -1235,18 +1273,11 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 	bool is_cow;
 	int ret;
 
-	/*
-	 * Don't copy ptes where a page fault will fill them correctly.
-	 * Fork becomes much lighter when there are big shared or private
-	 * readonly mappings. The tradeoff is that copy_page_range is more
-	 * efficient than faulting.
-	 */
-	if (!(src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) &&
-	    !src_vma->anon_vma)
+	if (!vma_needs_copy(dst_vma, src_vma))
 		return 0;
 
 	if (is_vm_hugetlb_page(src_vma))
-		return copy_hugetlb_page_range(dst_mm, src_mm, src_vma);
+		return copy_hugetlb_page_range(dst_mm, src_mm, dst_vma, src_vma);
 
 	if (unlikely(src_vma->vm_flags & VM_PFNMAP)) {
 		/*
@@ -1308,6 +1339,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 struct zap_details {
 	struct folio *single_folio;	/* Locked folio to be unmapped */
 	bool even_cows;			/* Zap COWed private pages too? */
+	zap_flags_t zap_flags;		/* Extra flags for zapping */
 };
 
 /* Whether we should zap all COWed (private) pages too */
@@ -1336,6 +1368,29 @@ static inline bool should_zap_page(struct zap_details *details, struct page *pag
 	return !PageAnon(page);
 }
 
+static inline bool zap_drop_file_uffd_wp(struct zap_details *details)
+{
+	if (!details)
+		return false;
+
+	return details->zap_flags & ZAP_FLAG_DROP_MARKER;
+}
+
+/*
+ * This function makes sure that we'll replace the none pte with an uffd-wp
+ * swap special pte marker when necessary. Must be with the pgtable lock held.
+ */
+static inline void
+zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
+			      unsigned long addr, pte_t *pte,
+			      struct zap_details *details, pte_t pteval)
+{
+	if (zap_drop_file_uffd_wp(details))
+		return;
+
+	pte_install_uffd_wp_if_needed(vma, addr, pte, pteval);
+}
+
 static unsigned long zap_pte_range(struct mmu_gather *tlb,
 				struct vm_area_struct *vma, pmd_t *pmd,
 				unsigned long addr, unsigned long end,
@@ -1373,6 +1428,8 @@ again:
 			ptent = ptep_get_and_clear_full(mm, addr, pte,
 							tlb->fullmm);
 			tlb_remove_tlb_entry(tlb, pte, addr);
+			zap_install_uffd_wp_if_needed(vma, addr, pte, details,
+						      ptent);
 			if (unlikely(!page))
 				continue;
 
@@ -1403,6 +1460,13 @@ again:
 			page = pfn_swap_entry_to_page(entry);
 			if (unlikely(!should_zap_page(details, page)))
 				continue;
+			/*
+			 * Both device private/exclusive mappings should only
+			 * work with anonymous page so far, so we don't need to
+			 * consider uffd-wp bit when zap. For more information,
+			 * see zap_install_uffd_wp_if_needed().
+			 */
+			WARN_ON_ONCE(!vma_is_anonymous(vma));
 			rss[mm_counter(page)]--;
 			if (is_device_private_entry(entry))
 				page_remove_rmap(page, vma, false);
@@ -1419,6 +1483,10 @@ again:
 			if (!should_zap_page(details, page))
 				continue;
 			rss[mm_counter(page)]--;
+		} else if (pte_marker_entry_uffd_wp(entry)) {
+			/* Only drop the uffd-wp marker if explicitly requested */
+			if (!zap_drop_file_uffd_wp(details))
+				continue;
 		} else if (is_hwpoison_entry(entry)) {
 			if (!should_zap_cows(details))
 				continue;
@@ -1427,6 +1495,7 @@ again:
 			WARN_ON_ONCE(1);
 		}
 		pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
+		zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
 	} while (pte++, addr += PAGE_SIZE, addr != end);
 
 	add_mm_rss_vec(mm, rss);
@@ -1605,8 +1674,11 @@ static void unmap_single_vma(struct mmu_gather *tlb,
 			 * safe to do nothing in this case.
 			 */
 			if (vma->vm_file) {
+				zap_flags_t zap_flags = details ?
+				    details->zap_flags : 0;
 				i_mmap_lock_write(vma->vm_file->f_mapping);
-				__unmap_hugepage_range_final(tlb, vma, start, end, NULL);
+				__unmap_hugepage_range_final(tlb, vma, start, end,
+							     NULL, zap_flags);
 				i_mmap_unlock_write(vma->vm_file->f_mapping);
 			}
 		} else
@@ -1637,12 +1709,17 @@ void unmap_vmas(struct mmu_gather *tlb,
 		unsigned long end_addr)
 {
 	struct mmu_notifier_range range;
+	struct zap_details details = {
+		.zap_flags = ZAP_FLAG_DROP_MARKER,
+		/* Careful - we need to zap private pages too! */
+		.even_cows = true,
+	};
 
 	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
 				start_addr, end_addr);
 	mmu_notifier_invalidate_range_start(&range);
 	for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next)
-		unmap_single_vma(tlb, vma, start_addr, end_addr, NULL);
+		unmap_single_vma(tlb, vma, start_addr, end_addr, &details);
 	mmu_notifier_invalidate_range_end(&range);
 }
 
@@ -2755,8 +2832,8 @@ static inline int pte_unmap_same(struct vm_fault *vmf)
 	return same;
 }
 
-static inline bool cow_user_page(struct page *dst, struct page *src,
-				 struct vm_fault *vmf)
+static inline bool __wp_page_copy_user(struct page *dst, struct page *src,
+				       struct vm_fault *vmf)
 {
 	bool ret;
 	void *kaddr;
@@ -2963,6 +3040,10 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
 	struct vm_area_struct *vma = vmf->vma;
 	struct page *page = vmf->page;
 	pte_t entry;
+
+	VM_BUG_ON(!(vmf->flags & FAULT_FLAG_WRITE));
+	VM_BUG_ON(PageAnon(page) && !PageAnonExclusive(page));
+
 	/*
 	 * Clear the pages cpupid information as the existing
 	 * information potentially belongs to a now completely
@@ -2981,7 +3062,8 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
 }
 
 /*
- * Handle the case of a page which we actually need to copy to a new page.
+ * Handle the case of a page which we actually need to copy to a new page,
+ * either due to COW or unsharing.
  *
  * Called with mmap_lock locked and the old page referenced, but
  * without the ptl held.
@@ -2998,6 +3080,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
  */
 static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 {
+	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
 	struct vm_area_struct *vma = vmf->vma;
 	struct mm_struct *mm = vma->vm_mm;
 	struct page *old_page = vmf->page;
@@ -3020,7 +3103,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		if (!new_page)
 			goto oom;
 
-		if (!cow_user_page(new_page, old_page, vmf)) {
+		if (!__wp_page_copy_user(new_page, old_page, vmf)) {
 			/*
 			 * COW failed, if the fault was solved by other,
 			 * it's fine. If not, userspace would re-fault on
@@ -3062,7 +3145,14 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
 		entry = mk_pte(new_page, vma->vm_page_prot);
 		entry = pte_sw_mkyoung(entry);
-		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		if (unlikely(unshare)) {
+			if (pte_soft_dirty(vmf->orig_pte))
+				entry = pte_mksoft_dirty(entry);
+			if (pte_uffd_wp(vmf->orig_pte))
+				entry = pte_mkuffd_wp(entry);
+		} else {
+			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		}
 
 		/*
 		 * Clear the pte entry and flush it first, before updating the
@@ -3072,13 +3162,14 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		 * some TLBs while the old PTE remains in others.
 		 */
 		ptep_clear_flush_notify(vma, vmf->address, vmf->pte);
-		page_add_new_anon_rmap(new_page, vma, vmf->address, false);
+		page_add_new_anon_rmap(new_page, vma, vmf->address);
 		lru_cache_add_inactive_or_unevictable(new_page, vma);
 		/*
 		 * We call the notify macro here because, when using secondary
 		 * mmu page tables (such as kvm shadow page tables), we want the
 		 * new page to be mapped directly into the secondary page table.
 		 */
+		BUG_ON(unshare && pte_write(entry));
 		set_pte_at_notify(mm, vmf->address, vmf->pte, entry);
 		update_mmu_cache(vma, vmf->address, vmf->pte);
 		if (old_page) {
@@ -3128,7 +3219,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 			free_swap_cache(old_page);
 		put_page(old_page);
 	}
-	return page_copied ? VM_FAULT_WRITE : 0;
+	return (page_copied && !unshare) ? VM_FAULT_WRITE : 0;
 oom_free_new:
 	put_page(new_page);
 oom:
@@ -3228,18 +3319,22 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
 }
 
 /*
- * This routine handles present pages, when users try to write
- * to a shared page. It is done by copying the page to a new address
- * and decrementing the shared-page counter for the old page.
+ * This routine handles present pages, when
+ * * users try to write to a shared page (FAULT_FLAG_WRITE)
+ * * GUP wants to take a R/O pin on a possibly shared anonymous page
+ *   (FAULT_FLAG_UNSHARE)
+ *
+ * It is done by copying the page to a new address and decrementing the
+ * shared-page counter for the old page.
  *
  * Note that this routine assumes that the protection checks have been
  * done by the caller (the low-level page fault routine in most cases).
- * Thus we can safely just mark it writable once we've done any necessary
- * COW.
+ * Thus, with FAULT_FLAG_WRITE, we can safely just mark it writable once we've
+ * done any necessary COW.
  *
- * We also mark the page dirty at this point even though the page will
- * change only once the write actually happens. This avoids a few races,
- * and potentially makes it more efficient.
+ * In case of FAULT_FLAG_WRITE, we also mark the page dirty at this point even
+ * though the page will change only once the write actually happens. This
+ * avoids a few races, and potentially makes it more efficient.
  *
  * We enter with non-exclusive mmap_lock (to exclude vma changes,
  * but allow concurrent faults), with pte both mapped and locked.
@@ -3248,23 +3343,35 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
 static vm_fault_t do_wp_page(struct vm_fault *vmf)
 	__releases(vmf->ptl)
 {
+	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
 	struct vm_area_struct *vma = vmf->vma;
 
-	if (userfaultfd_pte_wp(vma, *vmf->pte)) {
-		pte_unmap_unlock(vmf->pte, vmf->ptl);
-		return handle_userfault(vmf, VM_UFFD_WP);
-	}
+	VM_BUG_ON(unshare && (vmf->flags & FAULT_FLAG_WRITE));
+	VM_BUG_ON(!unshare && !(vmf->flags & FAULT_FLAG_WRITE));
 
-	/*
-	 * Userfaultfd write-protect can defer flushes. Ensure the TLB
-	 * is flushed in this case before copying.
-	 */
-	if (unlikely(userfaultfd_wp(vmf->vma) &&
-		     mm_tlb_flush_pending(vmf->vma->vm_mm)))
-		flush_tlb_page(vmf->vma, vmf->address);
+	if (likely(!unshare)) {
+		if (userfaultfd_pte_wp(vma, *vmf->pte)) {
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			return handle_userfault(vmf, VM_UFFD_WP);
+		}
+
+		/*
+		 * Userfaultfd write-protect can defer flushes. Ensure the TLB
+		 * is flushed in this case before copying.
+		 */
+		if (unlikely(userfaultfd_wp(vmf->vma) &&
+			     mm_tlb_flush_pending(vmf->vma->vm_mm)))
+			flush_tlb_page(vmf->vma, vmf->address);
+	}
 
 	vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte);
 	if (!vmf->page) {
+		if (unlikely(unshare)) {
+			/* No anonymous page -> nothing to do. */
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			return 0;
+		}
+
 		/*
 		 * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
 		 * VM_PFNMAP VMA.
@@ -3288,6 +3395,13 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
 		struct page *page = vmf->page;
 
 		/*
+		 * If the page is exclusive to this process we must reuse the
+		 * page without further checks.
+		 */
+		if (PageAnonExclusive(page))
+			goto reuse;
+
+		/*
 		 * We have to verify under page lock: these early checks are
 		 * just an optimization to avoid locking the page and freeing
 		 * the swapcache if there is little hope that we can reuse.
@@ -3317,9 +3431,19 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
 		 * and the page is locked, it's dark out, and we're wearing
 		 * sunglasses. Hit it.
 		 */
+		page_move_anon_rmap(page, vma);
 		unlock_page(page);
+reuse:
+		if (unlikely(unshare)) {
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			return 0;
+		}
 		wp_page_reuse(vmf);
 		return VM_FAULT_WRITE;
+	} else if (unshare) {
+		/* No anonymous page -> nothing to do. */
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return 0;
 	} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
 					(VM_WRITE|VM_SHARED))) {
 		return wp_page_shared(vmf);
@@ -3331,6 +3455,10 @@ copy:
 	get_page(vmf->page);
 
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
+#ifdef CONFIG_KSM
+	if (PageKsm(vmf->page))
+		count_vm_event(COW_KSM);
+#endif
 	return wp_page_copy(vmf);
 }
 
@@ -3387,6 +3515,7 @@ void unmap_mapping_folio(struct folio *folio)
 
 	details.even_cows = false;
 	details.single_folio = folio;
+	details.zap_flags = ZAP_FLAG_DROP_MARKER;
 
 	i_mmap_lock_read(mapping);
 	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
@@ -3508,6 +3637,59 @@ static inline bool should_try_to_free_swap(struct page *page,
 		page_count(page) == 2;
 }
 
+static vm_fault_t pte_marker_clear(struct vm_fault *vmf)
+{
+	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd,
+				       vmf->address, &vmf->ptl);
+	/*
+	 * Be careful so that we will only recover a special uffd-wp pte into a
+	 * none pte.  Otherwise it means the pte could have changed, so retry.
+	 */
+	if (is_pte_marker(*vmf->pte))
+		pte_clear(vmf->vma->vm_mm, vmf->address, vmf->pte);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return 0;
+}
+
+/*
+ * This is actually a page-missing access, but with uffd-wp special pte
+ * installed.  It means this pte was wr-protected before being unmapped.
+ */
+static vm_fault_t pte_marker_handle_uffd_wp(struct vm_fault *vmf)
+{
+	/*
+	 * Just in case there're leftover special ptes even after the region
+	 * got unregistered - we can simply clear them.  We can also do that
+	 * proactively when e.g. when we do UFFDIO_UNREGISTER upon some uffd-wp
+	 * ranges, but it should be more efficient to be done lazily here.
+	 */
+	if (unlikely(!userfaultfd_wp(vmf->vma) || vma_is_anonymous(vmf->vma)))
+		return pte_marker_clear(vmf);
+
+	/* do_fault() can handle pte markers too like none pte */
+	return do_fault(vmf);
+}
+
+static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
+{
+	swp_entry_t entry = pte_to_swp_entry(vmf->orig_pte);
+	unsigned long marker = pte_marker_get(entry);
+
+	/*
+	 * PTE markers should always be with file-backed memories, and the
+	 * marker should never be empty.  If anything weird happened, the best
+	 * thing to do is to kill the process along with its mm.
+	 */
+	if (WARN_ON_ONCE(vma_is_anonymous(vmf->vma) || !marker))
+		return VM_FAULT_SIGBUS;
+
+	if (pte_marker_entry_uffd_wp(entry))
+		return pte_marker_handle_uffd_wp(vmf);
+
+	/* This is an unknown pte marker */
+	return VM_FAULT_SIGBUS;
+}
+
 /*
  * We enter with non-exclusive mmap_lock (to exclude vma changes,
  * but allow concurrent faults), and pte mapped but not yet locked.
@@ -3521,10 +3703,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	struct vm_area_struct *vma = vmf->vma;
 	struct page *page = NULL, *swapcache;
 	struct swap_info_struct *si = NULL;
+	rmap_t rmap_flags = RMAP_NONE;
+	bool exclusive = false;
 	swp_entry_t entry;
 	pte_t pte;
 	int locked;
-	int exclusive = 0;
 	vm_fault_t ret = 0;
 	void *shadow = NULL;
 
@@ -3544,6 +3727,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 			ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
 		} else if (is_hwpoison_entry(entry)) {
 			ret = VM_FAULT_HWPOISON;
+		} else if (is_pte_marker_entry(entry)) {
+			ret = handle_pte_marker(vmf);
 		} else {
 			print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
 			ret = VM_FAULT_SIGBUS;
@@ -3585,7 +3770,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 				/* To provide entry to swap_readpage() */
 				set_page_private(page, entry.val);
-				swap_readpage(page, true);
+				swap_readpage(page, true, NULL);
 				set_page_private(page, 0);
 			}
 		} else {
@@ -3677,6 +3862,57 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	}
 
 	/*
+	 * PG_anon_exclusive reuses PG_mappedtodisk for anon pages. A swap pte
+	 * must never point at an anonymous page in the swapcache that is
+	 * PG_anon_exclusive. Sanity check that this holds and especially, that
+	 * no filesystem set PG_mappedtodisk on a page in the swapcache. Sanity
+	 * check after taking the PT lock and making sure that nobody
+	 * concurrently faulted in this page and set PG_anon_exclusive.
+	 */
+	BUG_ON(!PageAnon(page) && PageMappedToDisk(page));
+	BUG_ON(PageAnon(page) && PageAnonExclusive(page));
+
+	/*
+	 * Check under PT lock (to protect against concurrent fork() sharing
+	 * the swap entry concurrently) for certainly exclusive pages.
+	 */
+	if (!PageKsm(page)) {
+		/*
+		 * Note that pte_swp_exclusive() == false for architectures
+		 * without __HAVE_ARCH_PTE_SWP_EXCLUSIVE.
+		 */
+		exclusive = pte_swp_exclusive(vmf->orig_pte);
+		if (page != swapcache) {
+			/*
+			 * We have a fresh page that is not exposed to the
+			 * swapcache -> certainly exclusive.
+			 */
+			exclusive = true;
+		} else if (exclusive && PageWriteback(page) &&
+			  data_race(si->flags & SWP_STABLE_WRITES)) {
+			/*
+			 * This is tricky: not all swap backends support
+			 * concurrent page modifications while under writeback.
+			 *
+			 * So if we stumble over such a page in the swapcache
+			 * we must not set the page exclusive, otherwise we can
+			 * map it writable without further checks and modify it
+			 * while still under writeback.
+			 *
+			 * For these problematic swap backends, simply drop the
+			 * exclusive marker: this is perfectly fine as we start
+			 * writeback only if we fully unmapped the page and
+			 * there are no unexpected references on the page after
+			 * unmapping succeeded. After fully unmapped, no
+			 * further GUP references (FOLL_GET and FOLL_PIN) can
+			 * appear, so dropping the exclusive marker and mapping
+			 * it only R/O is fine.
+			 */
+			exclusive = false;
+		}
+	}
+
+	/*
 	 * Remove the swap entry and conditionally try to free up the swapcache.
 	 * We're already holding a reference on the page but haven't mapped it
 	 * yet.
@@ -3690,16 +3926,18 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	pte = mk_pte(page, vma->vm_page_prot);
 
 	/*
-	 * Same logic as in do_wp_page(); however, optimize for fresh pages
-	 * that are certainly not shared because we just allocated them without
-	 * exposing them to the swapcache.
+	 * Same logic as in do_wp_page(); however, optimize for pages that are
+	 * certainly not shared either because we just allocated them without
+	 * exposing them to the swapcache or because the swap entry indicates
+	 * exclusivity.
 	 */
-	if ((vmf->flags & FAULT_FLAG_WRITE) && !PageKsm(page) &&
-	    (page != swapcache || page_count(page) == 1)) {
-		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
-		vmf->flags &= ~FAULT_FLAG_WRITE;
-		ret |= VM_FAULT_WRITE;
-		exclusive = RMAP_EXCLUSIVE;
+	if (!PageKsm(page) && (exclusive || page_count(page) == 1)) {
+		if (vmf->flags & FAULT_FLAG_WRITE) {
+			pte = maybe_mkwrite(pte_mkdirty(pte), vma);
+			vmf->flags &= ~FAULT_FLAG_WRITE;
+			ret |= VM_FAULT_WRITE;
+		}
+		rmap_flags |= RMAP_EXCLUSIVE;
 	}
 	flush_icache_page(vma, page);
 	if (pte_swp_soft_dirty(vmf->orig_pte))
@@ -3712,12 +3950,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 
 	/* ksm created a completely new copy */
 	if (unlikely(page != swapcache && swapcache)) {
-		page_add_new_anon_rmap(page, vma, vmf->address, false);
+		page_add_new_anon_rmap(page, vma, vmf->address);
 		lru_cache_add_inactive_or_unevictable(page, vma);
 	} else {
-		do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
+		page_add_anon_rmap(page, vma, vmf->address, rmap_flags);
 	}
 
+	VM_BUG_ON(!PageAnon(page) || (pte_write(pte) && !PageAnonExclusive(page)));
 	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
 	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
 
@@ -3862,7 +4101,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	}
 
 	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
-	page_add_new_anon_rmap(page, vma, vmf->address, false);
+	page_add_new_anon_rmap(page, vma, vmf->address);
 	lru_cache_add_inactive_or_unevictable(page, vma);
 setpte:
 	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
@@ -4032,6 +4271,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
 void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
 {
 	struct vm_area_struct *vma = vmf->vma;
+	bool uffd_wp = pte_marker_uffd_wp(vmf->orig_pte);
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 	bool prefault = vmf->address != addr;
 	pte_t entry;
@@ -4046,10 +4286,12 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
 
 	if (write)
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	if (unlikely(uffd_wp))
+		entry = pte_mkuffd_wp(pte_wrprotect(entry));
 	/* copy-on-write page */
 	if (write && !(vma->vm_flags & VM_SHARED)) {
 		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
-		page_add_new_anon_rmap(page, vma, addr, false);
+		page_add_new_anon_rmap(page, vma, addr);
 		lru_cache_add_inactive_or_unevictable(page, vma);
 	} else {
 		inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
@@ -4058,6 +4300,14 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
 	set_pte_at(vma->vm_mm, addr, vmf->pte, entry);
 }
 
+static bool vmf_pte_changed(struct vm_fault *vmf)
+{
+	if (vmf->flags & FAULT_FLAG_ORIG_PTE_VALID)
+		return !pte_same(*vmf->pte, vmf->orig_pte);
+
+	return !pte_none(*vmf->pte);
+}
+
 /**
  * finish_fault - finish page fault once we have prepared the page to fault
  *
@@ -4116,7 +4366,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 				      vmf->address, &vmf->ptl);
 	ret = 0;
 	/* Re-check under ptl */
-	if (likely(pte_none(*vmf->pte)))
+	if (likely(!vmf_pte_changed(vmf)))
 		do_set_pte(vmf, page, vmf->address);
 	else
 		ret = VM_FAULT_NOPAGE;
@@ -4219,9 +4469,21 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf)
 	return vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff);
 }
 
+/* Return true if we should do read fault-around, false otherwise */
+static inline bool should_fault_around(struct vm_fault *vmf)
+{
+	/* No ->map_pages?  No way to fault around... */
+	if (!vmf->vma->vm_ops->map_pages)
+		return false;
+
+	if (uffd_disable_fault_around(vmf->vma))
+		return false;
+
+	return fault_around_bytes >> PAGE_SHIFT > 1;
+}
+
 static vm_fault_t do_read_fault(struct vm_fault *vmf)
 {
-	struct vm_area_struct *vma = vmf->vma;
 	vm_fault_t ret = 0;
 
 	/*
@@ -4229,12 +4491,10 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
 	 * if page by the offset is not ready to be mapped (cold cache or
 	 * something).
 	 */
-	if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
-		if (likely(!userfaultfd_minor(vmf->vma))) {
-			ret = do_fault_around(vmf);
-			if (ret)
-				return ret;
-		}
+	if (should_fault_around(vmf)) {
+		ret = do_fault_around(vmf);
+		if (ret)
+			return ret;
 	}
 
 	ret = __do_fault(vmf);
@@ -4504,8 +4764,11 @@ static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
 /* `inline' is required to avoid gcc 4.1.2 build error */
 static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
 {
+	const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
+
 	if (vma_is_anonymous(vmf->vma)) {
-		if (userfaultfd_huge_pmd_wp(vmf->vma, vmf->orig_pmd))
+		if (likely(!unshare) &&
+		    userfaultfd_huge_pmd_wp(vmf->vma, vmf->orig_pmd))
 			return handle_userfault(vmf, VM_UFFD_WP);
 		return do_huge_pmd_wp_page(vmf);
 	}
@@ -4581,6 +4844,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 		 * concurrent faults and from rmap lookups.
 		 */
 		vmf->pte = NULL;
+		vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID;
 	} else {
 		/*
 		 * If a huge pmd materialized under us just retry later.  Use
@@ -4604,6 +4868,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 		 */
 		vmf->pte = pte_offset_map(vmf->pmd, vmf->address);
 		vmf->orig_pte = *vmf->pte;
+		vmf->flags |= FAULT_FLAG_ORIG_PTE_VALID;
 
 		/*
 		 * some architectures can have larger ptes than wordsize,
@@ -4640,10 +4905,11 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 		update_mmu_tlb(vmf->vma, vmf->address, vmf->pte);
 		goto unlock;
 	}
-	if (vmf->flags & FAULT_FLAG_WRITE) {
+	if (vmf->flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) {
 		if (!pte_write(entry))
 			return do_wp_page(vmf);
-		entry = pte_mkdirty(entry);
+		else if (likely(vmf->flags & FAULT_FLAG_WRITE))
+			entry = pte_mkdirty(entry);
 	}
 	entry = pte_mkyoung(entry);
 	if (ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
@@ -4684,7 +4950,6 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
 		.pgoff = linear_page_index(vma, address),
 		.gfp_mask = __get_fault_gfp_mask(vma),
 	};
-	unsigned int dirty = flags & FAULT_FLAG_WRITE;
 	struct mm_struct *mm = vma->vm_mm;
 	pgd_t *pgd;
 	p4d_t *p4d;
@@ -4709,9 +4974,11 @@ retry_pud:
 		barrier();
 		if (pud_trans_huge(orig_pud) || pud_devmap(orig_pud)) {
 
-			/* NUMA case for anonymous PUDs would go here */
-
-			if (dirty && !pud_write(orig_pud)) {
+			/*
+			 * TODO once we support anonymous PUDs: NUMA case and
+			 * FAULT_FLAG_UNSHARE handling.
+			 */
+			if ((flags & FAULT_FLAG_WRITE) && !pud_write(orig_pud)) {
 				ret = wp_huge_pud(&vmf, orig_pud);
 				if (!(ret & VM_FAULT_FALLBACK))
 					return ret;
@@ -4749,7 +5016,8 @@ retry_pud:
 			if (pmd_protnone(vmf.orig_pmd) && vma_is_accessible(vma))
 				return do_huge_pmd_numa_page(&vmf);
 
-			if (dirty && !pmd_write(vmf.orig_pmd)) {
+			if ((flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) &&
+			    !pmd_write(vmf.orig_pmd)) {
 				ret = wp_huge_pmd(&vmf);
 				if (!(ret & VM_FAULT_FALLBACK))
 					return ret;
@@ -4949,9 +5217,29 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
 
-int follow_invalidate_pte(struct mm_struct *mm, unsigned long address,
-			  struct mmu_notifier_range *range, pte_t **ptepp,
-			  pmd_t **pmdpp, spinlock_t **ptlp)
+/**
+ * follow_pte - look up PTE at a user virtual address
+ * @mm: the mm_struct of the target address space
+ * @address: user virtual address
+ * @ptepp: location to store found PTE
+ * @ptlp: location to store the lock for the PTE
+ *
+ * On a successful return, the pointer to the PTE is stored in @ptepp;
+ * the corresponding lock is taken and its location is stored in @ptlp.
+ * The contents of the PTE are only stable until @ptlp is released;
+ * any further use, if any, must be protected against invalidation
+ * with MMU notifiers.
+ *
+ * Only IO mappings and raw PFN mappings are allowed.  The mmap semaphore
+ * should be taken for read.
+ *
+ * KVM uses this function.  While it is arguably less bad than ``follow_pfn``,
+ * it is not a good general-purpose API.
+ *
+ * Return: zero on success, -ve otherwise.
+ */
+int follow_pte(struct mm_struct *mm, unsigned long address,
+	       pte_t **ptepp, spinlock_t **ptlp)
 {
 	pgd_t *pgd;
 	p4d_t *p4d;
@@ -4974,35 +5262,9 @@ int follow_invalidate_pte(struct mm_struct *mm, unsigned long address,
 	pmd = pmd_offset(pud, address);
 	VM_BUG_ON(pmd_trans_huge(*pmd));
 
-	if (pmd_huge(*pmd)) {
-		if (!pmdpp)
-			goto out;
-
-		if (range) {
-			mmu_notifier_range_init(range, MMU_NOTIFY_CLEAR, 0,
-						NULL, mm, address & PMD_MASK,
-						(address & PMD_MASK) + PMD_SIZE);
-			mmu_notifier_invalidate_range_start(range);
-		}
-		*ptlp = pmd_lock(mm, pmd);
-		if (pmd_huge(*pmd)) {
-			*pmdpp = pmd;
-			return 0;
-		}
-		spin_unlock(*ptlp);
-		if (range)
-			mmu_notifier_invalidate_range_end(range);
-	}
-
 	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
 		goto out;
 
-	if (range) {
-		mmu_notifier_range_init(range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
-					address & PAGE_MASK,
-					(address & PAGE_MASK) + PAGE_SIZE);
-		mmu_notifier_invalidate_range_start(range);
-	}
 	ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
 	if (!pte_present(*ptep))
 		goto unlock;
@@ -5010,38 +5272,9 @@ int follow_invalidate_pte(struct mm_struct *mm, unsigned long address,
 	return 0;
 unlock:
 	pte_unmap_unlock(ptep, *ptlp);
-	if (range)
-		mmu_notifier_invalidate_range_end(range);
 out:
 	return -EINVAL;
 }
-
-/**
- * follow_pte - look up PTE at a user virtual address
- * @mm: the mm_struct of the target address space
- * @address: user virtual address
- * @ptepp: location to store found PTE
- * @ptlp: location to store the lock for the PTE
- *
- * On a successful return, the pointer to the PTE is stored in @ptepp;
- * the corresponding lock is taken and its location is stored in @ptlp.
- * The contents of the PTE are only stable until @ptlp is released;
- * any further use, if any, must be protected against invalidation
- * with MMU notifiers.
- *
- * Only IO mappings and raw PFN mappings are allowed.  The mmap semaphore
- * should be taken for read.
- *
- * KVM uses this function.  While it is arguably less bad than ``follow_pfn``,
- * it is not a good general-purpose API.
- *
- * Return: zero on success, -ve otherwise.
- */
-int follow_pte(struct mm_struct *mm, unsigned long address,
-	       pte_t **ptepp, spinlock_t **ptlp)
-{
-	return follow_invalidate_pte(mm, address, NULL, ptepp, NULL, ptlp);
-}
 EXPORT_SYMBOL_GPL(follow_pte);
 
 /**