1 files changed, 50 insertions, 10 deletions

diff --git a/mm/gup.c b/mm/gup.c
index 6297f6bcc..a798293fc 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -12,7 +12,9 @@
 #include <linux/sched.h>
 #include <linux/rwsem.h>
 #include <linux/hugetlb.h>
+
 #include <asm/pgtable.h>
+#include <asm/tlbflush.h>
 
 #include "internal.h"
 
@@ -32,6 +34,30 @@ static struct page *no_page_table(struct vm_area_struct *vma,
 	return NULL;
 }
 
+static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
+		pte_t *pte, unsigned int flags)
+{
+	/* No page to get reference */
+	if (flags & FOLL_GET)
+		return -EFAULT;
+
+	if (flags & FOLL_TOUCH) {
+		pte_t entry = *pte;
+
+		if (flags & FOLL_WRITE)
+			entry = pte_mkdirty(entry);
+		entry = pte_mkyoung(entry);
+
+		if (!pte_same(*pte, entry)) {
+			set_pte_at(vma->vm_mm, address, pte, entry);
+			update_mmu_cache(vma, address, pte);
+		}
+	}
+
+	/* Proper page table entry exists, but no corresponding struct page */
+	return -EEXIST;
+}
+
 static struct page *follow_page_pte(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd, unsigned int flags)
 {
@@ -73,10 +99,21 @@ retry:
 
 	page = vm_normal_page(vma, address, pte);
 	if (unlikely(!page)) {
-		if ((flags & FOLL_DUMP) ||
-		    !is_zero_pfn(pte_pfn(pte)))
-			goto bad_page;
-		page = pte_page(pte);
+		if (flags & FOLL_DUMP) {
+			/* Avoid special (like zero) pages in core dumps */
+			page = ERR_PTR(-EFAULT);
+			goto out;
+		}
+
+		if (is_zero_pfn(pte_pfn(pte))) {
+			page = pte_page(pte);
+		} else {
+			int ret;
+
+			ret = follow_pfn_pte(vma, address, ptep, flags);
+			page = ERR_PTR(ret);
+			goto out;
+		}
 	}
 
 	if (flags & FOLL_GET)
@@ -114,12 +151,9 @@ retry:
 			unlock_page(page);
 		}
 	}
+out:
 	pte_unmap_unlock(ptep, ptl);
 	return page;
-bad_page:
-	pte_unmap_unlock(ptep, ptl);
-	return ERR_PTR(-EFAULT);
-
 no_page:
 	pte_unmap_unlock(ptep, ptl);
 	if (!pte_none(pte))
@@ -489,9 +523,15 @@ retry:
 				goto next_page;
 			}
 			BUG();
-		}
-		if (IS_ERR(page))
+		} else if (PTR_ERR(page) == -EEXIST) {
+			/*
+			 * Proper page table entry exists, but no corresponding
+			 * struct page.
+			 */
+			goto next_page;
+		} else if (IS_ERR(page)) {
 			return i ? i : PTR_ERR(page);
+		}
 		if (pages) {
 			pages[i] = page;
 			flush_anon_page(vma, page, start);