Re: FAILED: patch "[PATCH] migrate: hugetlb: check for hugetlb shared PMD in node" failed to apply to 4.19-stable tree

[Mike Kravetz <mike.kravetz@oracle.com>]

On 02/07/23 10:16, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 4.19-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Updated patch below.  Note that this depends on backport of upstream
commit 3489dbb696d25602aea8c3e669a6d43b76bd5358 which is already queued
up for 4.19-stable tree.

From 8f863a8bae356277b55b2ff909a52d12be5398a6 Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@oracle.com>
Date: Thu, 26 Jan 2023 14:27:21 -0800
Subject: [PATCH] migrate: hugetlb: check for hugetlb shared PMD in node
 migration

commit 73bdf65ea74857d7fb2ec3067a3cec0e261b1462 upstream.

migrate_pages/mempolicy semantics state that CAP_SYS_NICE is required to
move pages shared with another process to a different node.  page_mapcount
> 1 is being used to determine if a hugetlb page is shared.  However, a
hugetlb page will have a mapcount of 1 if mapped by multiple processes via
a shared PMD.  As a result, hugetlb pages shared by multiple processes and
mapped with a shared PMD can be moved by a process without CAP_SYS_NICE.

To fix, check for a shared PMD if mapcount is 1.  If a shared PMD is found
consider the page shared.

Link: https://lkml.kernel.org/r/20230126222721.222195-3-mike.kravetz@oracle.com
Fixes: e2d8cf405525 ("migrate: add hugepage migration code to migrate_pages()")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/mempolicy.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e44e737e90a3..35088e830bff 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -571,7 +571,8 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long hmask,
 		goto unlock;
 	/* With MPOL_MF_MOVE, we migrate only unshared hugepage. */
 	if (flags & (MPOL_MF_MOVE_ALL) ||
-	    (flags & MPOL_MF_MOVE && page_mapcount(page) == 1))
+	    (flags & MPOL_MF_MOVE && page_mapcount(page) == 1 &&
+	     !hugetlb_pmd_shared(pte)))
 		isolate_huge_page(page, qp->pagelist);
 unlock:
 	spin_unlock(ptl);
-- 
2.39.1