Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | "Fabio M. De Francesco" <> | Subject | [PATCH] mm/ksm: Use kmap_local_page() in calc_checksum() | Date | Mon, 20 Nov 2023 15:18:44 +0100 |
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From: "Fabio M. De Francesco" <fabio.maria.de.francesco@intel.com>
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()).
Cc: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com> --- mm/ksm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c index 6a831009b4cb..5d60d5385de6 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1099,9 +1099,9 @@ static int unmerge_and_remove_all_rmap_items(void) 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; } -- 2.42.0
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