Patch "mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-thp-do-not-make-page-table-dirty-unconditionally-in-touch_pd.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Kirill A. Shutemov" <[email protected]>
Date: Mon, 27 Nov 2017 06:21:25 +0300
Subject: mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d()

From: Kirill A. Shutemov <[email protected]>

commit a8f97366452ed491d13cf1e44241bc0b5740b1f0 upstream.

Currently, we unconditionally make page table dirty in touch_pmd(). It may result in false-positive can_follow_write_pmd().

We may avoid the situation, if we would only make the page table entry dirty if caller asks for write access -- FOLL_WRITE.

The patch also changes touch_pud() in the same way.

[Salvatore Bonaccorso: backport for 4.9:
- Adjust context
- Drop specific part for PUD-sized transparent hugepages. Support for PUD-sized transparent hugepages was added in v4.11-rc1
]

---
 mm/huge_memory.c |   19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

@@ -745,20 +745,15 @@ int vmf_insert_pfn_pmd(struct vm_area_st
 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
 
 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
-		pmd_t *pmd)
+		pmd_t *pmd, int flags)
 {
 	pmd_t _pmd;
 
-	/*
-	 * We should set the dirty bit only for FOLL_WRITE but for now
-	 * the dirty bit in the pmd is meaningless.  And if the dirty
-	 * bit will become meaningful and we'll only set it with
-	 * FOLL_WRITE, an atomic set_bit will be required on the pmd to
-	 * set the young bit, instead of the current set_pmd_at.
-	 */
-	_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
+	_pmd = pmd_mkyoung(*pmd);
+	if (flags & FOLL_WRITE)
+		_pmd = pmd_mkdirty(_pmd);
 	if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
-				pmd, _pmd,  1))
+				pmd, _pmd, flags & FOLL_WRITE))
 		update_mmu_cache_pmd(vma, addr, pmd);
 }
 

@@ -787,7 +782,7 @@ struct page *follow_devmap_pmd(struct vm
 		return NULL;
 
 	if (flags & FOLL_TOUCH)
-		touch_pmd(vma, addr, pmd);
+		touch_pmd(vma, addr, pmd, flags);
 
 	/*
 	 * device mapped pages can only be returned if the

@@ -1158,7 +1153,7 @@ struct page *follow_trans_huge_pmd(struc
 	page = pmd_page(*pmd);
 	VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
 	if (flags & FOLL_TOUCH)
-		touch_pmd(vma, addr, pmd);
+		touch_pmd(vma, addr, pmd, flags);
 	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
 		/*
 		 * We don't mlock() pte-mapped THPs. This way we can avoid

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-thp-do-not-make-page-table-dirty-unconditionally-in-touch_pd.patch queue-4.9/mm-madvise.c-fix-madvise-infinite-loop-under-special-circumstances.patch