diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index a1341fdcf666..5d1e3c980f74 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -218,9 +218,9 @@ void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud,
 
 int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags,
 		     int advice);
-int madvise_collapse(struct vm_area_struct *vma,
-		     struct vm_area_struct **prev,
-		     unsigned long start, unsigned long end);
+int madvise_collapse_thp(struct vm_area_struct *vma,
+			 struct vm_area_struct **prev,
+			 unsigned long start, unsigned long end);
 void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start,
 			   unsigned long end, long adjust_next);
 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma);
@@ -367,9 +367,9 @@ static inline int hugepage_madvise(struct vm_area_struct *vma,
 	return -EINVAL;
 }
 
-static inline int madvise_collapse(struct vm_area_struct *vma,
-				   struct vm_area_struct **prev,
-				   unsigned long start, unsigned long end)
+static inline int madvise_collapse_thp(struct vm_area_struct *vma,
+				       struct vm_area_struct **prev,
+				       unsigned long start, unsigned long end)
 {
 	return -EINVAL;
 }
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c8524ac49b24..e1baf939afb6 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1298,6 +1298,8 @@ bool hugetlb_hgm_eligible(struct vm_area_struct *vma);
 int hugetlb_alloc_largest_pte(struct hugetlb_pte *hpte, struct mm_struct *mm,
 			      struct vm_area_struct *vma, unsigned long start,
 			      unsigned long end);
+int hugetlb_collapse(struct mm_struct *mm, struct vm_area_struct *vma,
+		     unsigned long start, unsigned long end);
 #else
 static inline bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
 {
@@ -1318,6 +1320,12 @@ int hugetlb_alloc_largest_pte(struct hugetlb_pte *hpte, struct mm_struct *mm,
 {
 	return -EINVAL;
 }
+static inline
+int hugetlb_collapse(struct mm_struct *mm, struct vm_area_struct *vma,
+		     unsigned long start, unsigned long end)
+{
+	return -EINVAL;
+}
 #endif
 
 static inline spinlock_t *huge_pte_lock(struct hstate *h,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5b6215e03fe1..388c46c7e77a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -7852,6 +7852,170 @@ int hugetlb_alloc_largest_pte(struct hugetlb_pte *hpte, struct mm_struct *mm,
 	return 0;
 }
 
+static bool hugetlb_hgm_collapsable(struct vm_area_struct *vma)
+{
+	if (!hugetlb_hgm_eligible(vma))
+		return false;
+	if (!vma->vm_private_data)	/* vma lock required for collapsing */
+		return false;
+	return true;
+}
+
+/*
+ * Collapse the address range from @start to @end to be mapped optimally.
+ *
+ * This is only valid for shared mappings. The main use case for this function
+ * is following UFFDIO_CONTINUE. If a user UFFDIO_CONTINUEs an entire hugepage
+ * by calling UFFDIO_CONTINUE once for each 4K region, the kernel doesn't know
+ * to collapse the mapping after the final UFFDIO_CONTINUE. Instead, we leave
+ * it up to userspace to tell us to do so, via MADV_COLLAPSE.
+ *
+ * Any holes in the mapping will be filled. If there is no page in the
+ * pagecache for a region we're collapsing, the PTEs will be cleared.
+ *
+ * If high-granularity PTEs are uffd-wp markers, those markers will be dropped.
+ */
+int hugetlb_collapse(struct mm_struct *mm, struct vm_area_struct *vma,
+			    unsigned long start, unsigned long end)
+{
+	struct hstate *h = hstate_vma(vma);
+	struct address_space *mapping = vma->vm_file->f_mapping;
+	struct mmu_notifier_range range;
+	struct mmu_gather tlb;
+	unsigned long curr = start;
+	int ret = 0;
+	struct page *hpage, *subpage;
+	pgoff_t idx;
+	bool writable = vma->vm_flags & VM_WRITE;
+	bool shared = vma->vm_flags & VM_SHARED;
+	struct hugetlb_pte hpte;
+	pte_t entry;
+
+	/*
+	 * This is only supported for shared VMAs, because we need to look up
+	 * the page to use for any PTEs we end up creating.
+	 */
+	if (!shared)
+		return -EINVAL;
+
+	/* If HGM is not enabled, there is nothing to collapse. */
+	if (!hugetlb_hgm_enabled(vma))
+		return 0;
+
+	/*
+	 * We lost the VMA lock after splitting, so we can't safely collapse.
+	 * We could improve this in the future (like take the mmap_lock for
+	 * writing and try again), but for now just fail with ENOMEM.
+	 */
+	if (unlikely(!hugetlb_hgm_collapsable(vma)))
+		return -ENOMEM;
+
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
+				start, end);
+	mmu_notifier_invalidate_range_start(&range);
+	tlb_gather_mmu(&tlb, mm);
+
+	/*
+	 * Grab the VMA lock and mapping sem for writing. This will prevent
+	 * concurrent high-granularity page table walks, so that we can safely
+	 * collapse and free page tables.
+	 *
+	 * This is the same locking that huge_pmd_unshare requires.
+	 */
+	hugetlb_vma_lock_write(vma);
+	i_mmap_lock_write(vma->vm_file->f_mapping);
+
+	while (curr < end) {
+		ret = hugetlb_alloc_largest_pte(&hpte, mm, vma, curr, end);
+		if (ret)
+			goto out;
+
+		entry = huge_ptep_get(hpte.ptep);
+
+		/*
+		 * There is no work to do if the PTE doesn't point to page
+		 * tables.
+		 */
+		if (!pte_present(entry))
+			goto next_hpte;
+		if (hugetlb_pte_present_leaf(&hpte, entry))
+			goto next_hpte;
+
+		idx = vma_hugecache_offset(h, vma, curr);
+		hpage = find_get_page(mapping, idx);
+
+		if (hpage && !HPageMigratable(hpage)) {
+			/*
+			 * Don't collapse a mapping to a page that is pending
+			 * a migration. Migration swap entries may have placed
+			 * in the page table.
+			 */
+			ret = -EBUSY;
+			put_page(hpage);
+			goto out;
+		}
+
+		if (hpage && PageHWPoison(hpage)) {
+			/*
+			 * Don't collapse a mapping to a page that is
+			 * hwpoisoned.
+			 */
+			ret = -EHWPOISON;
+			put_page(hpage);
+			/*
+			 * By setting ret to -EHWPOISON, if nothing else
+			 * happens, we will tell userspace that we couldn't
+			 * fully collapse everything due to poison.
+			 *
+			 * Skip this page, and continue to collapse the rest
+			 * of the mapping.
+			 */
+			curr = (curr & huge_page_mask(h)) + huge_page_size(h);
+			continue;
+		}
+
+		/*
+		 * Clear all the PTEs, and drop ref/mapcounts
+		 * (on tlb_finish_mmu).
+		 */
+		__unmap_hugepage_range(&tlb, vma, curr,
+			curr + hugetlb_pte_size(&hpte),
+			NULL,
+			ZAP_FLAG_DROP_MARKER);
+		/* Free the PTEs. */
+		hugetlb_free_pgd_range(&tlb,
+				curr, curr + hugetlb_pte_size(&hpte),
+				curr, curr + hugetlb_pte_size(&hpte));
+		if (!hpage) {
+			huge_pte_clear(mm, curr, hpte.ptep,
+					hugetlb_pte_size(&hpte));
+			goto next_hpte;
+		}
+
+		page_dup_file_rmap(hpage, true);
+
+		subpage = hugetlb_find_subpage(h, hpage, curr);
+		entry = make_huge_pte_with_shift(vma, subpage,
+						 writable, hpte.shift);
+		set_huge_pte_at(mm, curr, hpte.ptep, entry);
+next_hpte:
+		curr += hugetlb_pte_size(&hpte);
+
+		if (curr < end) {
+			/* Don't hold the VMA lock for too long. */
+			hugetlb_vma_unlock_write(vma);
+			cond_resched();
+			hugetlb_vma_lock_write(vma);
+		}
+	}
+out:
+	i_mmap_unlock_write(vma->vm_file->f_mapping);
+	hugetlb_vma_unlock_write(vma);
+	tlb_finish_mmu(&tlb);
+	mmu_notifier_invalidate_range_end(&range);
+	return ret;
+}
+
 #endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
 
 /*
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index e1c7c1f357ef..cbeb7f00f1bf 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2718,8 +2718,8 @@ static int madvise_collapse_errno(enum scan_result r)
 	}
 }
 
-int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
-		     unsigned long start, unsigned long end)
+int madvise_collapse_thp(struct vm_area_struct *vma, struct vm_area_struct **prev,
+			 unsigned long start, unsigned long end)
 {
 	struct collapse_control *cc;
 	struct mm_struct *mm = vma->vm_mm;
diff --git a/mm/madvise.c b/mm/madvise.c
index 04ee28992e52..fec47e9f845b 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1029,6 +1029,18 @@ static int madvise_split(struct vm_area_struct *vma,
 	return 0;
 }
 
+static int madvise_collapse(struct vm_area_struct *vma,
+			    struct vm_area_struct **prev,
+			    unsigned long start, unsigned long end)
+{
+	if (is_vm_hugetlb_page(vma)) {
+		*prev = vma;
+		return hugetlb_collapse(vma->vm_mm, vma, start, end);
+	}
+
+	return madvise_collapse_thp(vma, prev, start, end);
+}
+
 /*
  * Apply an madvise behavior to a region of a vma.  madvise_update_vma
  * will handle splitting a vm area into separate areas, each area with its own
@@ -1205,6 +1217,9 @@ madvise_behavior_valid(int behavior)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	case MADV_HUGEPAGE:
 	case MADV_NOHUGEPAGE:
+#endif
+#if defined(CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING) || \
+		defined(CONFIG_TRANSPARENT_HUGEPAGE)
 	case MADV_COLLAPSE:
 #endif
 #ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
@@ -1398,7 +1413,8 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
  *  MADV_NOHUGEPAGE - mark the given range as not worth being backed by
  *		transparent huge pages so the existing pages will not be
  *		coalesced into THP and new pages will not be allocated as THP.
- *  MADV_COLLAPSE - synchronously coalesce pages into new THP.
+ *  MADV_COLLAPSE - synchronously coalesce pages into new THP, or, for HugeTLB
+ *		pages, collapse the mapping.
  *  MADV_DONTDUMP - the application wants to prevent pages in the given range
  *		from being included in its core dump.
  *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
