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mm/util: use kmap_local_page() in memcmp_pages()

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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@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>
This commit is contained in:
Fabio De Francesco 2023-11-20 15:15:27 +01:00 committed by Andrew Morton
parent 95a2ac9370
commit 2f7537620f
1 changed files with 4 additions and 4 deletions
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8
mm/util.c
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@ -1047,11 +1047,11 @@ int __weak memcmp_pages(struct page *page1, struct page *page2)
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;
}