The patch titled
Subject: mm/util: use kmap_local_page() in memcmp_pages()
has been added to the -mm mm-unstable branch. Its filename is
mm-util-use-kmap_local_page-in-memcmp_pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-util-use-kmap_local_page-in-memcmp_pages.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 De Francesco <fabio.maria.de.francesco@xxxxxxxxx>
Subject: mm/util: use kmap_local_page() in memcmp_pages()
Date: Mon, 20 Nov 2023 15:15:27 +0100
kmap_atomic() has been deprecated in favor of kmap_local_page().
Therefore, replace kmap_atomic() with kmap_local_page() in memcmp_pages().
kmap_atomic() is implemented like a kmap_local_page() which also disables
page-faults and preemption (the latter only in !PREEMPT_RT kernels). The
kernel virtual addresses returned by these two API are only valid in the
context of the callers (i.e., they cannot be handed to other threads).
With kmap_local_page() the mappings are per thread and CPU local like in
kmap_atomic(); however, they can handle page-faults and can be called from
any context (including interrupts). The tasks that call kmap_local_page()
can be preempted and, when they are scheduled to run again, the kernel
virtual addresses are restored and are still valid.
In memcmp_pages(), the block of code between the mapping and un-mapping
does not depend on the above-mentioned side effects of kmap_aatomic(), so
that mere replacements of the old API with the new one is all that is
required (i.e., there is no need to explicitly call pagefault_disable()
and/or preempt_disable()).
Link: https://lkml.kernel.org/r/20231120141554.6612-1-fmdefrancesco@xxxxxxxxx
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@xxxxxxxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/util.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/mm/util.c~mm-util-use-kmap_local_page-in-memcmp_pages
+++ a/mm/util.c
@@ -1047,11 +1047,11 @@ int __weak memcmp_pages(struct page *pag
char *addr1, *addr2;
int ret;
- addr1 = kmap_atomic(page1);
- addr2 = kmap_atomic(page2);
+ addr1 = kmap_local_page(page1);
+ addr2 = kmap_local_page(page2);
ret = memcmp(addr1, addr2, PAGE_SIZE);
- kunmap_atomic(addr2);
- kunmap_atomic(addr1);
+ kunmap_local(addr2);
+ kunmap_local(addr1);
return ret;
}
_
Patches currently in -mm which might be from fabio.maria.de.francesco@xxxxxxxxx are
mm-util-use-kmap_local_page-in-memcmp_pages.patch
mm-ksm-use-kmap_local_page-in-calc_checksum.patch
