proc/pid/pagemap: correctly report non-present ptes and holes between vmas

Reset the current pagemap-entry if the current pte isn't present, or if
current vma is over.  Otherwise pagemap reports last entry again and
again.

Non-present pte reporting was broken in commit 092b50bacd1c ("pagemap:
introduce data structure for pagemap entry")

Reporting for holes was broken in commit 5aaabe831eb5 ("pagemap: avoid
splitting thp when reading /proc/pid/pagemap")

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Reported-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/task_mmu.c

@@ -747,6 +747,8 @@ static void pte_to_pagemap_entry(pagemap_entry_t *pme, pte_t pte)
 	else if (pte_present(pte))
 		*pme = make_pme(PM_PFRAME(pte_pfn(pte))
 				| PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT);
+	else
+		*pme = make_pme(PM_NOT_PRESENT);
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -761,6 +763,8 @@ static void thp_pmd_to_pagemap_entry(pagemap_entry_t *pme,
 	if (pmd_present(pmd))
 		*pme = make_pme(PM_PFRAME(pmd_pfn(pmd) + offset)
 				| PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT);
+	else
+		*pme = make_pme(PM_NOT_PRESENT);
 }
 #else
 static inline void thp_pmd_to_pagemap_entry(pagemap_entry_t *pme,
@@ -801,8 +805,10 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 
 		/* check to see if we've left 'vma' behind
 		 * and need a new, higher one */
-		if (vma && (addr >= vma->vm_end))
+		if (vma && (addr >= vma->vm_end)) {
 			vma = find_vma(walk->mm, addr);
+			pme = make_pme(PM_NOT_PRESENT);
+		}
 
 		/* check that 'vma' actually covers this address,
 		 * and that it isn't a huge page vma */
@@ -830,6 +836,8 @@ static void huge_pte_to_pagemap_entry(pagemap_entry_t *pme,
 	if (pte_present(pte))
 		*pme = make_pme(PM_PFRAME(pte_pfn(pte) + offset)
 				| PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT);
+	else
+		*pme = make_pme(PM_NOT_PRESENT);
 }
 
 /* This function walks within one hugetlb entry in the single call */
@@ -839,7 +847,7 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
 {
 	struct pagemapread *pm = walk->private;
 	int err = 0;
-	pagemap_entry_t pme = make_pme(PM_NOT_PRESENT);
+	pagemap_entry_t pme;
 
 	for (; addr != end; addr += PAGE_SIZE) {
 		int offset = (addr & ~hmask) >> PAGE_SHIFT;