[PATCH 5.4.y 1/2] mm/mempool: replace kmap_atomic() with kmap_local_page()

[Sasha Levin <sashal@kernel.org>]

From: "Fabio M. De Francesco" <fabio.maria.de.francesco@linux.intel.com>

[ Upstream commit f2bcc99a5e901a13b754648d1dbab60f4adf9375 ]

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

Therefore, replace kmap_atomic() with kmap_local_page().

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.

The code blocks between the mappings and un-mappings don't rely on the
above-mentioned side effects of kmap_atomic(), so that mere replacements
of the old API with the new one is all that they require (i.e., there is
no need to explicitly call pagefault_disable() and/or preempt_disable()).

Link: https://lkml.kernel.org/r/20231120142640.7077-1-fabio.maria.de.francesco@linux.intel.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>
Stable-dep-of: ec33b59542d9 ("mm/mempool: fix poisoning order>0 pages with HIGHMEM")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/mempool.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/mempool.c b/mm/mempool.c
index 85efab3da7204..f9f2afe42b92a 100644
--- a/mm/mempool.c
+++ b/mm/mempool.c
@@ -64,10 +64,10 @@ static void check_element(mempool_t *pool, void *element)
 	/* Mempools backed by page allocator */
 	if (pool->free == mempool_free_pages) {
 		int order = (int)(long)pool->pool_data;
-		void *addr = kmap_atomic((struct page *)element);
+		void *addr = kmap_local_page((struct page *)element);
 
 		__check_element(pool, addr, 1UL << (PAGE_SHIFT + order));
-		kunmap_atomic(addr);
+		kunmap_local(addr);
 	}
 }
 
@@ -88,10 +88,10 @@ static void poison_element(mempool_t *pool, void *element)
 	/* Mempools backed by page allocator */
 	if (pool->alloc == mempool_alloc_pages) {
 		int order = (int)(long)pool->pool_data;
-		void *addr = kmap_atomic((struct page *)element);
+		void *addr = kmap_local_page((struct page *)element);
 
 		__poison_element(addr, 1UL << (PAGE_SHIFT + order));
-		kunmap_atomic(addr);
+		kunmap_local(addr);
 	}
 }
 #else /* CONFIG_DEBUG_SLAB || CONFIG_SLUB_DEBUG_ON */
-- 
2.51.0