v4.19.13 snapshot.
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
new file mode 100644
index 0000000..c3084ff
--- /dev/null
+++ b/mm/pagewalk.c
@@ -0,0 +1,358 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/sched.h>
+#include <linux/hugetlb.h>
+
+static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ pte_t *pte;
+ int err = 0;
+
+ pte = pte_offset_map(pmd, addr);
+ for (;;) {
+ err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
+ if (err)
+ break;
+ addr += PAGE_SIZE;
+ if (addr == end)
+ break;
+ pte++;
+ }
+
+ pte_unmap(pte);
+ return err;
+}
+
+static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ pmd_t *pmd;
+ unsigned long next;
+ int err = 0;
+
+ pmd = pmd_offset(pud, addr);
+ do {
+again:
+ next = pmd_addr_end(addr, end);
+ if (pmd_none(*pmd) || !walk->vma) {
+ if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+ if (err)
+ break;
+ continue;
+ }
+ /*
+ * This implies that each ->pmd_entry() handler
+ * needs to know about pmd_trans_huge() pmds
+ */
+ if (walk->pmd_entry)
+ err = walk->pmd_entry(pmd, addr, next, walk);
+ if (err)
+ break;
+
+ /*
+ * Check this here so we only break down trans_huge
+ * pages when we _need_ to
+ */
+ if (!walk->pte_entry)
+ continue;
+
+ split_huge_pmd(walk->vma, pmd, addr);
+ if (pmd_trans_unstable(pmd))
+ goto again;
+ err = walk_pte_range(pmd, addr, next, walk);
+ if (err)
+ break;
+ } while (pmd++, addr = next, addr != end);
+
+ return err;
+}
+
+static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ pud_t *pud;
+ unsigned long next;
+ int err = 0;
+
+ pud = pud_offset(p4d, addr);
+ do {
+ again:
+ next = pud_addr_end(addr, end);
+ if (pud_none(*pud) || !walk->vma) {
+ if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+ if (err)
+ break;
+ continue;
+ }
+
+ if (walk->pud_entry) {
+ spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
+
+ if (ptl) {
+ err = walk->pud_entry(pud, addr, next, walk);
+ spin_unlock(ptl);
+ if (err)
+ break;
+ continue;
+ }
+ }
+
+ split_huge_pud(walk->vma, pud, addr);
+ if (pud_none(*pud))
+ goto again;
+
+ if (walk->pmd_entry || walk->pte_entry)
+ err = walk_pmd_range(pud, addr, next, walk);
+ if (err)
+ break;
+ } while (pud++, addr = next, addr != end);
+
+ return err;
+}
+
+static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ p4d_t *p4d;
+ unsigned long next;
+ int err = 0;
+
+ p4d = p4d_offset(pgd, addr);
+ do {
+ next = p4d_addr_end(addr, end);
+ if (p4d_none_or_clear_bad(p4d)) {
+ if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+ if (err)
+ break;
+ continue;
+ }
+ if (walk->pmd_entry || walk->pte_entry)
+ err = walk_pud_range(p4d, addr, next, walk);
+ if (err)
+ break;
+ } while (p4d++, addr = next, addr != end);
+
+ return err;
+}
+
+static int walk_pgd_range(unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ pgd_t *pgd;
+ unsigned long next;
+ int err = 0;
+
+ pgd = pgd_offset(walk->mm, addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ if (pgd_none_or_clear_bad(pgd)) {
+ if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+ if (err)
+ break;
+ continue;
+ }
+ if (walk->pmd_entry || walk->pte_entry)
+ err = walk_p4d_range(pgd, addr, next, walk);
+ if (err)
+ break;
+ } while (pgd++, addr = next, addr != end);
+
+ return err;
+}
+
+#ifdef CONFIG_HUGETLB_PAGE
+static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
+ unsigned long end)
+{
+ unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
+ return boundary < end ? boundary : end;
+}
+
+static int walk_hugetlb_range(unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ struct vm_area_struct *vma = walk->vma;
+ struct hstate *h = hstate_vma(vma);
+ unsigned long next;
+ unsigned long hmask = huge_page_mask(h);
+ unsigned long sz = huge_page_size(h);
+ pte_t *pte;
+ int err = 0;
+
+ do {
+ next = hugetlb_entry_end(h, addr, end);
+ pte = huge_pte_offset(walk->mm, addr & hmask, sz);
+
+ if (pte)
+ err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
+ else if (walk->pte_hole)
+ err = walk->pte_hole(addr, next, walk);
+
+ if (err)
+ break;
+ } while (addr = next, addr != end);
+
+ return err;
+}
+
+#else /* CONFIG_HUGETLB_PAGE */
+static int walk_hugetlb_range(unsigned long addr, unsigned long end,
+ struct mm_walk *walk)
+{
+ return 0;
+}
+
+#endif /* CONFIG_HUGETLB_PAGE */
+
+/*
+ * Decide whether we really walk over the current vma on [@start, @end)
+ * or skip it via the returned value. Return 0 if we do walk over the
+ * current vma, and return 1 if we skip the vma. Negative values means
+ * error, where we abort the current walk.
+ */
+static int walk_page_test(unsigned long start, unsigned long end,
+ struct mm_walk *walk)
+{
+ struct vm_area_struct *vma = walk->vma;
+
+ if (walk->test_walk)
+ return walk->test_walk(start, end, walk);
+
+ /*
+ * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
+ * range, so we don't walk over it as we do for normal vmas. However,
+ * Some callers are interested in handling hole range and they don't
+ * want to just ignore any single address range. Such users certainly
+ * define their ->pte_hole() callbacks, so let's delegate them to handle
+ * vma(VM_PFNMAP).
+ */
+ if (vma->vm_flags & VM_PFNMAP) {
+ int err = 1;
+ if (walk->pte_hole)
+ err = walk->pte_hole(start, end, walk);
+ return err ? err : 1;
+ }
+ return 0;
+}
+
+static int __walk_page_range(unsigned long start, unsigned long end,
+ struct mm_walk *walk)
+{
+ int err = 0;
+ struct vm_area_struct *vma = walk->vma;
+
+ if (vma && is_vm_hugetlb_page(vma)) {
+ if (walk->hugetlb_entry)
+ err = walk_hugetlb_range(start, end, walk);
+ } else
+ err = walk_pgd_range(start, end, walk);
+
+ return err;
+}
+
+/**
+ * walk_page_range - walk page table with caller specific callbacks
+ * @start: start address of the virtual address range
+ * @end: end address of the virtual address range
+ * @walk: mm_walk structure defining the callbacks and the target address space
+ *
+ * Recursively walk the page table tree of the process represented by @walk->mm
+ * within the virtual address range [@start, @end). During walking, we can do
+ * some caller-specific works for each entry, by setting up pmd_entry(),
+ * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
+ * callbacks, the associated entries/pages are just ignored.
+ * The return values of these callbacks are commonly defined like below:
+ *
+ * - 0 : succeeded to handle the current entry, and if you don't reach the
+ * end address yet, continue to walk.
+ * - >0 : succeeded to handle the current entry, and return to the caller
+ * with caller specific value.
+ * - <0 : failed to handle the current entry, and return to the caller
+ * with error code.
+ *
+ * Before starting to walk page table, some callers want to check whether
+ * they really want to walk over the current vma, typically by checking
+ * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
+ * purpose.
+ *
+ * struct mm_walk keeps current values of some common data like vma and pmd,
+ * which are useful for the access from callbacks. If you want to pass some
+ * caller-specific data to callbacks, @walk->private should be helpful.
+ *
+ * Locking:
+ * Callers of walk_page_range() and walk_page_vma() should hold
+ * @walk->mm->mmap_sem, because these function traverse vma list and/or
+ * access to vma's data.
+ */
+int walk_page_range(unsigned long start, unsigned long end,
+ struct mm_walk *walk)
+{
+ int err = 0;
+ unsigned long next;
+ struct vm_area_struct *vma;
+
+ if (start >= end)
+ return -EINVAL;
+
+ if (!walk->mm)
+ return -EINVAL;
+
+ VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);
+
+ vma = find_vma(walk->mm, start);
+ do {
+ if (!vma) { /* after the last vma */
+ walk->vma = NULL;
+ next = end;
+ } else if (start < vma->vm_start) { /* outside vma */
+ walk->vma = NULL;
+ next = min(end, vma->vm_start);
+ } else { /* inside vma */
+ walk->vma = vma;
+ next = min(end, vma->vm_end);
+ vma = vma->vm_next;
+
+ err = walk_page_test(start, next, walk);
+ if (err > 0) {
+ /*
+ * positive return values are purely for
+ * controlling the pagewalk, so should never
+ * be passed to the callers.
+ */
+ err = 0;
+ continue;
+ }
+ if (err < 0)
+ break;
+ }
+ if (walk->vma || walk->pte_hole)
+ err = __walk_page_range(start, next, walk);
+ if (err)
+ break;
+ } while (start = next, start < end);
+ return err;
+}
+
+int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk)
+{
+ int err;
+
+ if (!walk->mm)
+ return -EINVAL;
+
+ VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
+ VM_BUG_ON(!vma);
+ walk->vma = vma;
+ err = walk_page_test(vma->vm_start, vma->vm_end, walk);
+ if (err > 0)
+ return 0;
+ if (err < 0)
+ return err;
+ return __walk_page_range(vma->vm_start, vma->vm_end, walk);
+}