mm/smaps: Don't access young/dirty bit if pte unpresent

These bits should only be valid when the ptes are present. Introducing two booleans for it and set it to false when !pte_present() for both pte and pmd accountings.

The bug is found during code reading and no real world issue reported, but logically such an error can cause incorrect readings for either smaps or smaps_rollup output on quite a few fields.

For example, it could cause over-estimate on values like Shared_Dirty, Private_Dirty, Referenced. Or it could also cause under-estimate on values like LazyFree, Shared_Clean, Private_Clean.

Cc Konstantin Khlebnikov <[email protected]>

Cc Huang Ying <[email protected]>

Fixes b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries")

Fixes c94b6923fa0a ("/proc/PID/smaps: Add PMD migration entry parsing")

Reviewed-by Vlastimil Babka <[email protected]>

Reviewed-by David Hildenbrand <[email protected]>

Reviewed-by Yang Shi <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 fs/proc/task_mmu.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

fs/proc/task_mmu.c +8 -6

index 9913f3be9fd2..d56c65f98d00 100644
@@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	struct vm_area_struct *vma = walk->vma;
 	bool locked = !!(vma->vm_flags & VM_LOCKED);
 	struct page *page = NULL;
-	bool migration = false;
+	bool migration = false, young = false, dirty = false;
 
 	if (pte_present(*pte)) {
 		page = vm_normal_page(vma, addr, *pte);
+		young = pte_young(*pte);
+		dirty = pte_dirty(*pte);
 	} else if (is_swap_pte(*pte)) {
 		swp_entry_t swpent = pte_to_swp_entry(*pte);
 

@@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	if (!page)
 		return;
 
-	smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
-		      locked, migration);
+	smaps_account(mss, page, false, young, dirty, locked, migration);
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE

@@ -572,11 +573,13 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 	struct vm_area_struct *vma = walk->vma;
 	bool locked = !!(vma->vm_flags & VM_LOCKED);
 	struct page *page = NULL;
-	bool migration = false;
+	bool migration = false, young = false, dirty = false;
 
 	if (pmd_present(*pmd)) {
 		/* FOLL_DUMP will return -EFAULT on huge zero page */
 		page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
+		young = pmd_young(*pmd);
+		dirty = pmd_dirty(*pmd);
 	} else if (unlikely(thp_migration_supported() && is_swap_pmd(*pmd))) {
 		swp_entry_t entry = pmd_to_swp_entry(*pmd);
 

@@ -596,8 +599,7 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 	else
 		mss->file_thp += HPAGE_PMD_SIZE;
 
-	smaps_account(mss, page, true, pmd_young(*pmd), pmd_dirty(*pmd),
-		      locked, migration);
+	smaps_account(mss, page, true, young, dirty, locked, migration);
 }
 #else
 static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,