+ mm-memory-use-kmap_local_page-in-__wp_page_copy_user.patch added to mm-unstable branch

+ mm-memory-use-kmap_local_page-in-__wp_page_copy_user.patch added to mm-unstable branch

[Andrew Morton]

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

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-use-kmap_local_page-in-__wp_page_copy_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: "Fabio M. De Francesco" <fabio.maria.de.francesco@linux.intel.com>
Subject: mm/memory: use kmap_local_page() in __wp_page_copy_user()
Date: Mon, 20 Nov 2023 15:24:05 +0100

kmap_atomic() has been deprecated in favor of kmap_local_{folio,page}.

Therefore, replace kmap_atomic() with kmap_local_page in
__wp_page_copy_user().

kmap_atomic() disables preemption in !PREEMPT_RT kernels and
unconditionally disables also page-faults.  My limited knowledge of the
implementation of __wp_page_copy_user() makes me think that the latter
side effect is still needed here, but kmap_local_page() is implemented not
to disable page-faults.

So, in addition to the conversion to local mapping, add explicit
pagefault_disable() / pagefault_enable() between mapping and un-mapping.

Link: https://lkml.kernel.org/r/20231120142418.6977-1-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/memory.c~mm-memory-use-kmap_local_page-in-__wp_page_copy_user
+++ a/mm/memory.c
@@ -2841,7 +2841,8 @@ static inline int __wp_page_copy_user(st
 	 * just copying from the original user address. If that
 	 * fails, we just zero-fill it. Live with it.
 	 */
-	kaddr = kmap_atomic(dst);
+	kaddr = kmap_local_page(dst);
+	pagefault_disable();
 	uaddr = (void __user *)(addr & PAGE_MASK);
 
 	/*
@@ -2909,7 +2910,8 @@ warn:
 pte_unlock:
 	if (vmf->pte)
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
-	kunmap_atomic(kaddr);
+	pagefault_enable();
+	kunmap_local(kaddr);
 	flush_dcache_page(dst);
 
 	return ret;
_

Patches currently in -mm which might be from fabio.maria.de.francesco@linux.intel.com are

mm-memory-use-kmap_local_page-in-__wp_page_copy_user.patch
mm-mempool-replace-kmap_atomic-with-kmap_local_page.patch
mm-page_poison-replace-kmap_atomic-with-kmap_local_page.patch