3 files changed, 14 insertions, 32 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e41795bba95d..45ee5b5a343d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1231,7 +1231,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
 #define FOLL_WRITE      0x01    /* check pte is writable */
 #define FOLL_TOUCH      0x02    /* mark page accessed */
 #define FOLL_GET        0x04    /* do get_page on page */
-#define FOLL_ANON       0x08    /* give ZERO_PAGE if no pgtable */
+#define FOLL_DUMP       0x08    /* give error on hole if it would be zero */
 
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
                         void *data);
diff --git a/mm/internal.h b/mm/internal.h
index 166765cd58d6..d41475078b20 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -252,6 +252,7 @@ static inline void mminit_validate_memmodel_limits(unsigned long *start_pfn,
 
 #define GUP_FLAGS_WRITE         0x01
 #define GUP_FLAGS_FORCE         0x02
+#define GUP_FLAGS_DUMP          0x04
 
 int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                      unsigned long start, int len, int flags,
diff --git a/mm/memory.c b/mm/memory.c
index a8430ff13837..532a55bce6a4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1174,41 +1174,22 @@ no_page:
         pte_unmap_unlock(ptep, ptl);
         if (!pte_none(pte))
                 return page;
-        /* Fall through to ZERO_PAGE handling */
+
 no_page_table:
         /*
          * When core dumping an enormous anonymous area that nobody
-         * has touched so far, we don't want to allocate page tables.
+         * has touched so far, we don't want to allocate unnecessary pages or
+         * page tables.  Return error instead of NULL to skip handle_mm_fault,
+         * then get_dump_page() will return NULL to leave a hole in the dump.
+         * But we can only make this optimization where a hole would surely
+         * be zero-filled if handle_mm_fault() actually did handle it.
          */
-        if (flags & FOLL_ANON) {
-                page = ZERO_PAGE(0);
-                if (flags & FOLL_GET)
-                        get_page(page);
-                BUG_ON(flags & FOLL_WRITE);
-        }
+        if ((flags & FOLL_DUMP) &&
+            (!vma->vm_ops || !vma->vm_ops->fault))
+                return ERR_PTR(-EFAULT);
         return page;
 }
 
-/* Can we do the FOLL_ANON optimization? */
-static inline int use_zero_page(struct vm_area_struct *vma)
-{
-        /*
-         * We don't want to optimize FOLL_ANON for make_pages_present()
-         * when it tries to page in a VM_LOCKED region. As to VM_SHARED,
-         * we want to get the page from the page tables to make sure
-         * that we serialize and update with any other user of that
-         * mapping.
-         */
-        if (vma->vm_flags & (VM_LOCKED | VM_SHARED))
-                return 0;
-        /*
-         * And if we have a fault routine, it's not an anonymous region.
-         */
-        return !vma->vm_ops || !vma->vm_ops->fault;
-}
-
-
-
 int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                      unsigned long start, int nr_pages, int flags,
                      struct page **pages, struct vm_area_struct **vmas)
@@ -1288,8 +1269,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                 foll_flags = FOLL_TOUCH;
                 if (pages)
                         foll_flags |= FOLL_GET;
-                if (!write && use_zero_page(vma))
-                        foll_flags |= FOLL_ANON;
+                if (flags & GUP_FLAGS_DUMP)
+                        foll_flags |= FOLL_DUMP;
 
                 do {
                         struct page *page;
@@ -1446,7 +1427,7 @@ struct page *get_dump_page(unsigned long addr)
         struct page *page;
 
         if (__get_user_pages(current, current->mm, addr, 1,
-                                GUP_FLAGS_FORCE, &page, &vma) < 1)
+                        GUP_FLAGS_FORCE | GUP_FLAGS_DUMP, &page, &vma) < 1)
                 return NULL;
         if (page == ZERO_PAGE(0)) {
                 page_cache_release(page);