[RFC PATCH v4 7/8] hugetlb: create hugetlb_unmap_file_folio to unmap single file folio

[Mike Kravetz <mike.kravetz@oracle.com>]

Create the new routine hugetlb_unmap_file_folio that will unmap a single
file folio.  This is refactored code from hugetlb_vmdelete_list.  It is
modified to do locking within the routine itself and check whether the
page is mapped within a specific vma before unmapping.

This refactoring will be put to use and expanded upon in a subsequent
patch adding vma specific locking.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
 fs/hugetlbfs/inode.c | 124 +++++++++++++++++++++++++++++++++----------
 1 file changed, 95 insertions(+), 29 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 31bd4325fce5..0eac0ea2a245 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -396,6 +396,94 @@ static int hugetlbfs_write_end(struct file *file, struct address_space *mapping,
 	return -EINVAL;
 }
 
+/*
+ * Called with i_mmap_rwsem held for inode based vma maps.  This makes
+ * sure vma (and vm_mm) will not go away.  We also hold the hugetlb fault
+ * mutex for the page in the mapping.  So, we can not race with page being
+ * faulted into the vma.
+ */
+static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
+				unsigned long addr, struct page *page)
+{
+	pte_t *ptep, pte;
+
+	ptep = huge_pte_offset(vma->vm_mm, addr,
+			huge_page_size(hstate_vma(vma)));
+
+	if (!ptep)
+		return false;
+
+	pte = huge_ptep_get(ptep);
+	if (huge_pte_none(pte) || !pte_present(pte))
+		return false;
+
+	if (pte_page(pte) == page)
+		return true;
+
+	return false;	/* WTH??? */
+}
+
+/*
+ * Can vma_offset_start/vma_offset_end overflow on 32-bit arches?
+ * No, because the interval tree returns us only those vmas
+ * which overlap the truncated area starting at pgoff,
+ * and no vma on a 32-bit arch can span beyond the 4GB.
+ */
+static unsigned long vma_offset_start(struct vm_area_struct *vma, pgoff_t start)
+{
+	if (vma->vm_pgoff < start)
+		return (start - vma->vm_pgoff) << PAGE_SHIFT;
+	else
+		return 0;
+}
+
+static unsigned long vma_offset_end(struct vm_area_struct *vma, pgoff_t end)
+{
+	unsigned long t_end;
+
+	if (!end)
+		return vma->vm_end;
+
+	t_end = ((end - vma->vm_pgoff) << PAGE_SHIFT) + vma->vm_start;
+	if (t_end > vma->vm_end)
+		t_end = vma->vm_end;
+	return t_end;
+}
+
+/*
+ * Called with hugetlb fault mutex held.  Therefore, no more mappings to
+ * this folio can be created while executing the routine.
+ */
+static void hugetlb_unmap_file_folio(struct hstate *h,
+					struct address_space *mapping,
+					struct folio *folio, pgoff_t index)
+{
+	struct rb_root_cached *root = &mapping->i_mmap;
+	struct page *page = &folio->page;
+	struct vm_area_struct *vma;
+	unsigned long v_start;
+	unsigned long v_end;
+	pgoff_t start, end;
+
+	start = index * pages_per_huge_page(h);
+	end = ((index + 1) * pages_per_huge_page(h));
+
+	i_mmap_lock_write(mapping);
+
+	vma_interval_tree_foreach(vma, root, start, end - 1) {
+		v_start = vma_offset_start(vma, start);
+		v_end = vma_offset_end(vma, end);
+
+		if (!hugetlb_vma_maps_page(vma, vma->vm_start + v_start, page))
+			continue;
+
+		unmap_hugepage_range(vma, vma->vm_start + v_start, v_end,
+				NULL, ZAP_FLAG_DROP_MARKER);
+	}
+
+	i_mmap_unlock_write(mapping);
+}
+
 static void
 hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
 		      zap_flags_t zap_flags)
@@ -408,30 +496,13 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
 	 * an inclusive "last".
 	 */
 	vma_interval_tree_foreach(vma, root, start, end ? end - 1 : ULONG_MAX) {
-		unsigned long v_offset;
+		unsigned long v_start;
 		unsigned long v_end;
 
-		/*
-		 * Can the expression below overflow on 32-bit arches?
-		 * No, because the interval tree returns us only those vmas
-		 * which overlap the truncated area starting at pgoff,
-		 * and no vma on a 32-bit arch can span beyond the 4GB.
-		 */
-		if (vma->vm_pgoff < start)
-			v_offset = (start - vma->vm_pgoff) << PAGE_SHIFT;
-		else
-			v_offset = 0;
-
-		if (!end)
-			v_end = vma->vm_end;
-		else {
-			v_end = ((end - vma->vm_pgoff) << PAGE_SHIFT)
-							+ vma->vm_start;
-			if (v_end > vma->vm_end)
-				v_end = vma->vm_end;
-		}
+		v_start = vma_offset_start(vma, start);
+		v_end = vma_offset_end(vma, end);
 
-		unmap_hugepage_range(vma, vma->vm_start + v_offset, v_end,
+		unmap_hugepage_range(vma, vma->vm_start + v_start, v_end,
 				     NULL, zap_flags);
 	}
 }
@@ -504,14 +575,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 			 * the fault mutex.  The mutex will prevent faults
 			 * until we finish removing the folio.
 			 */
-			if (unlikely(folio_mapped(folio))) {
-				i_mmap_lock_write(mapping);
-				hugetlb_vmdelete_list(&mapping->i_mmap,
-					index * pages_per_huge_page(h),
-					(index + 1) * pages_per_huge_page(h),
-					ZAP_FLAG_DROP_MARKER);
-				i_mmap_unlock_write(mapping);
-			}
+			if (unlikely(folio_mapped(folio)))
+				hugetlb_unmap_file_folio(h, mapping, folio,
+							index);
 
 			folio_lock(folio);
 			/*
-- 
2.35.3