From a7f40cfe3b7ada57af9b62fd28430eeb4a7cfcb7 Mon Sep 17 00:00:00 2001

From: Yang Shi <yang.shi@linux.alibaba.com>

Date: Thu, 28 Mar 2019 20:43:55 -0700

Subject: [PATCH] mm: mempolicy: make mbind() return -EIO when MPOL_MF_STRICT

 is specified

Git-commit: a7f40cfe3b7ada57af9b62fd28430eeb4a7cfcb7

Patch-mainline: v5.1-rc3

References: bsc#1185906

mhocko@suse.com:

This kernel splits THPs rather than migrate them so we have to check for

the mode and bail out early if this is a pure MPOL_MF_STRICT mode

without move. Otherwise would would just have split the page and

potentially end up on a different node breaking the syscall contract.

When MPOL_MF_STRICT was specified and an existing page was already on a

node that does not follow the policy, mbind() should return -EIO.  But

commit 6f4576e3687b ("mempolicy: apply page table walker on

queue_pages_range()") broke the rule.

And commit c8633798497c ("mm: mempolicy: mbind and migrate_pages support

thp migration") didn't return the correct value for THP mbind() too.

If MPOL_MF_STRICT is set, ignore vma_migratable() to make sure it

reaches queue_pages_to_pte_range() or queue_pages_pmd() to check if an

existing page was already on a node that does not follow the policy.

And, non-migratable vma may be used, return -EIO too if MPOL_MF_MOVE or

MPOL_MF_MOVE_ALL was specified.

Tested with https://github.com/metan-ucw/ltp/blob/master/testcases/kernel/syscalls/mbind/mbind02.c

[akpm@linux-foundation.org: tweak code comment]

Link: http://lkml.kernel.org/r/1553020556-38583-1-git-send-email-yang.shi@linux.alibaba.com

Fixes: 6f4576e3687b ("mempolicy: apply page table walker on queue_pages_range()")

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>

Signed-off-by: Oscar Salvador <osalvador@suse.de>

Reported-by: Cyril Hrubis <chrubis@suse.cz>

Suggested-by: Kirill A. Shutemov <kirill@shutemov.name>

Acked-by: Rafael Aquini <aquini@redhat.com>

Reviewed-by: Oscar Salvador <osalvador@suse.de>

Acked-by: David Rientjes <rientjes@google.com>

Cc: Vlastimil Babka <vbabka@suse.cz>

Cc: <stable@vger.kernel.org>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Michal Hocko <mhocko@suse.com>

---

 mm/mempolicy.c |   53 +++++++++++++++++++++++++++++++++++++++++++++++------

 1 file changed, 47 insertions(+), 6 deletions(-)

--- a/mm/mempolicy.c

+++ b/mm/mempolicy.c

@@ -499,6 +499,22 @@ static int queue_pages_pte_range(pmd_t *

 		ptl = pmd_lock(walk->mm, pmd);

 		if (pmd_trans_huge(*pmd)) {

 			page = pmd_page(*pmd);

+

+			nid = page_to_nid(page);

+			if (node_isset(nid, *qp->nmask) == !!(flags & MPOL_MF_INVERT)) {

+				spin_unlock(ptl);

+				return 0;

+			}

+

+			/*

+			 * We cannot modify (split) THP in pure strict mode. A misplaced

+			 * page has to be reported by EIO

+			 */

+			if ((flags & (MPOL_MF_STRICT | MPOL_MF_MOVE | MPOL_MF_MOVE_ALL) == MPOL_MF_STRICT)) {

+				spin_unlock(ptl);

+				return -EIO;

+			}

+

 			if (is_huge_zero_page(page)) {

 				spin_unlock(ptl);

 				__split_huge_pmd(vma, pmd, addr, false, NULL);

@@ -509,8 +525,15 @@ static int queue_pages_pte_range(pmd_t *

 				ret = split_huge_page(page);

 				unlock_page(page);

 				put_page(page);

-				if (ret)

+				if (ret) {

+					/*

+					 * When moving pages in the strict mode we

+					 * should report errors

+					 */

+					if (flags & MPOL_MF_STRICT)

+						return -EIO;

 					return 0;

+				}

 			}

 		} else {

 			spin_unlock(ptl);

@@ -536,6 +559,12 @@ retry:

 		nid = page_to_nid(page);

 		if (node_isset(nid, *qp->nmask) == !!(flags & MPOL_MF_INVERT))

 			continue;

+		/*

+		 * We cannot modify (split) THP in pure strict mode. A misplaced

+		 * page has to be reported by EIO

+		 */

+		if ((flags & (MPOL_MF_STRICT | MPOL_MF_MOVE | MPOL_MF_MOVE_ALL) == MPOL_MF_STRICT))

+			break;

 		if (PageTransCompound(page)) {

 			get_page(page);

 			pte_unmap_unlock(pte, ptl);

@@ -543,8 +572,10 @@ retry:

 			ret = split_huge_page(page);

 			unlock_page(page);

 			put_page(page);

-			/* Failed to split -- skip. */

+			/* Failed to split -- skip. unless in strict mode */

 			if (ret) {

+				if (flags & MPOL_MF_STRICT)

+					return -EIO;

 				pte = pte_offset_map_lock(walk->mm, pmd,

 						addr, &ptl);

 				continue;

@@ -552,11 +583,16 @@ retry:

 			goto retry;

 		}

-		migrate_page_add(page, qp->pagelist, flags);

+		if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {

+			if (!vma_migratable(vma))

+				break;

+			migrate_page_add(page, qp->pagelist, flags);

+		} else

+			break;

 	}

 	pte_unmap_unlock(pte - 1, ptl);

 	cond_resched();

-	return 0;

+	return addr != end ? -EIO : 0;

 }

 static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,

@@ -628,7 +664,12 @@ static int queue_pages_test_walk(unsigne

 	unsigned long endvma = vma->vm_end;

 	unsigned long flags = qp->flags;

-	if (!vma_migratable(vma))

+	/*

+	 * Need check MPOL_MF_STRICT to return -EIO if possible

+	 * regardless of vma_migratable

+	 */

+	if (!vma_migratable(vma) &&

+	    !(flags & MPOL_MF_STRICT))

 		return 1;

 	if (endvma > end)

@@ -655,7 +696,7 @@ static int queue_pages_test_walk(unsigne

 	}

 	/* queue pages from current vma */

-	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))

+	if (flags & MPOL_MF_VALID)

 		return 0;

 	return 1;

 }