+ userfaultfd-use-kmap_local_page-in-copy_huge_page_from_user.patch added to mm-unstable branch

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The patch titled
     Subject: userfaultfd: use kmap_local_page() in copy_huge_page_from_user()
has been added to the -mm mm-unstable branch.  Its filename is
     userfaultfd-use-kmap_local_page-in-copy_huge_page_from_user.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/userfaultfd-use-kmap_local_page-in-copy_huge_page_from_user.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
Subject: userfaultfd: use kmap_local_page() in copy_huge_page_from_user()
Date: Fri, 31 Mar 2023 17:39:33 +0800

kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page() which is appropriate for any thread local context.[1]

Let's replace the kmap() and kmap_atomic() with kmap_local_page() in
copy_huge_page_from_user().  When allow_pagefault is false, disable page
faults to prevent potential deadlock.[2]

Link:https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@xxxxxxxxx/ [1]
Link: https://lkml.kernel.org/r/20221025220136.2366143-1-ira.weiny@xxxxxxxxx [2]
Link: https://lkml.kernel.org/r/20230331093937.945725-3-zhangpeng362@xxxxxxxxxx
Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nanyong Sun <sunnanyong@xxxxxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memory.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

--- a/mm/memory.c~userfaultfd-use-kmap_local_page-in-copy_huge_page_from_user
+++ a/mm/memory.c
@@ -5880,16 +5880,14 @@ long copy_huge_page_from_user(struct pag
 
 	for (i = 0; i < pages_per_huge_page; i++) {
 		subpage = nth_page(dst_page, i);
-		if (allow_pagefault)
-			page_kaddr = kmap(subpage);
-		else
-			page_kaddr = kmap_atomic(subpage);
+		page_kaddr = kmap_local_page(subpage);
+		if (!allow_pagefault)
+			pagefault_disable();
 		rc = copy_from_user(page_kaddr,
 				usr_src + i * PAGE_SIZE, PAGE_SIZE);
-		if (allow_pagefault)
-			kunmap(subpage);
-		else
-			kunmap_atomic(page_kaddr);
+		if (!allow_pagefault)
+			pagefault_enable();
+		kunmap_local(page_kaddr);
 
 		ret_val -= (PAGE_SIZE - rc);
 		if (rc)
_

Patches currently in -mm which might be from zhangpeng362@xxxxxxxxxx are

userfaultfd-convert-mfill_atomic_pte_copy-to-use-a-folio.patch
userfaultfd-use-kmap_local_page-in-copy_huge_page_from_user.patch
userfaultfd-convert-copy_huge_page_from_user-to-copy_folio_from_user.patch
userfaultfd-convert-mfill_atomic_hugetlb-to-use-a-folio.patch
mm-convert-copy_user_huge_page-to-copy_user_folio.patch
userfaultfd-convert-mfill_atomic-to-use-a-folio.patch




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