mm/ksm: use kmap_local_page() in calc_checksum()

kmap_atomic() has been deprecated in favor of kmap_local_page().

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

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 calc_checksum(), the block of code between the mapping and un-mapping
does not depend on the above-mentioned side effects of kmap_aatomic(), so
that a 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/20231120141855.6761-1-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>

diff --git a/mm/ksm.c b/mm/ksm.c
index 6a831009b4cbf9e191707571aacf0a6d4c8db7e1..5d60d5385de67a38da131a585d0e765bb9af5912 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1099,9 +1099,9 @@ error:
 static u32 calc_checksum(struct page *page)
 {
        u32 checksum;
-       void *addr = kmap_atomic(page);
+       void *addr = kmap_local_page(page);
        checksum = xxhash(addr, PAGE_SIZE, 0);
-       kunmap_atomic(addr);
+       kunmap_local(addr);
        return checksum;
 }