The patch titled
Subject: mm/userfaultfd: replace kmap/kmap_atomic() with kmap_local_page()
has been added to the -mm mm-unstable branch. Its filename is
mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Ira Weiny <ira.weiny@xxxxxxxxx>
Subject: mm/userfaultfd: replace kmap/kmap_atomic() with kmap_local_page()
Date: Sun, 23 Oct 2022 21:34:52 -0700
kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page() which is appropriate for any thread local context.[1]
A recent locking bug report with userfaultfd showed that the conversion of
these kmap_atomic()'s required care with regard to the prevention of
deadlock.[2]
Complete kmap conversion in userfaultfd by replacing the kmap() and
kmap_atomic() calls with kmap_local_page(). When replacing the
kmap_atomic() call ensure page faults continue to be disabled to support
the correct fall back behavior and add a comment to inform future souls of
the requirement.
[1] https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@xxxxxxxxx/
[2] https://lore.kernel.org/all/Y1Mh2S7fUGQ%2FiKFR@iweiny-desk3/
Link: https://lkml.kernel.org/r/20221024043452.1491677-1-ira.weiny@xxxxxxxxx
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/userfaultfd.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
--- a/mm/userfaultfd.c~mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page
+++ a/mm/userfaultfd.c
@@ -157,11 +157,18 @@ static int mcopy_atomic_pte(struct mm_st
if (!page)
goto out;
- page_kaddr = kmap_atomic(page);
+ page_kaddr = kmap_local_page(page);
+ /*
+ * The mmap_lock is held here. Disable page faults to
+ * prevent deadlock should copy_from_user() fault. The
+ * copy will be retried outside the mmap_lock.
+ */
+ pagefault_disable();
ret = copy_from_user(page_kaddr,
(const void __user *) src_addr,
PAGE_SIZE);
- kunmap_atomic(page_kaddr);
+ pagefault_enable();
+ kunmap_local(page_kaddr);
/* fallback to copy_from_user outside mmap_lock */
if (unlikely(ret)) {
@@ -646,11 +653,11 @@ retry:
mmap_read_unlock(dst_mm);
BUG_ON(!page);
- page_kaddr = kmap(page);
+ page_kaddr = kmap_local_page(page);
err = copy_from_user(page_kaddr,
(const void __user *) src_addr,
PAGE_SIZE);
- kunmap(page);
+ kunmap_local(page_kaddr);
if (unlikely(err)) {
err = -EFAULT;
goto out;
_
Patches currently in -mm which might be from ira.weiny@xxxxxxxxx are
mm-userfaultfd-replace-kmap-kmap_atomic-with-kmap_local_page.patch
