linux-kernel - [PATCH] pm: Replace deprecated kmap_atomic() with kmap_local

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Message-ID: <20250112015535.191527-1-me@davidreaver.com>
Date: Sat, 11 Jan 2025 17:55:32 -0800
From: David Reaver <me@...idreaver.com>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>
Cc: David Reaver <me@...idreaver.com>,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH] pm: Replace deprecated kmap_atomic() with kmap_local_page()

kmap_atomic() is deprecated and should be replaced with kmap_local_page()
[1][2]. kmap_local_page() is faster in kernels with HIGHMEM enabled, can
take page faults, and allows preemption.

According to [2], this replacement is safe as long as the code between
kmap_atomic() and kunmap_atomic() does not implicitly depend on disabling
page faults or preemption. In all of the call sites in this patch, the only
thing happening between mapping and unmapping pages is copy_page() calls,
and I don't suspect they depend on disabling page faults or preemption.

[1] https://lwn.net/Articles/836144/
[2] https://docs.kernel.org/mm/highmem.html#temporary-virtual-mappings

Signed-off-by: David Reaver <me@...idreaver.com>
---
 kernel/power/snapshot.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index c9fb559a6399..87f4dde4a49d 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -2270,9 +2270,9 @@ int snapshot_read_next(struct snapshot_handle *handle)
 			 */
 			void *kaddr;
 
-			kaddr = kmap_atomic(page);
+			kaddr = kmap_local_page(page);
 			copy_page(buffer, kaddr);
-			kunmap_atomic(kaddr);
+			kunmap_local(kaddr);
 			handle->buffer = buffer;
 		} else {
 			handle->buffer = page_address(page);
@@ -2561,9 +2561,9 @@ static void copy_last_highmem_page(void)
 	if (last_highmem_page) {
 		void *dst;
 
-		dst = kmap_atomic(last_highmem_page);
+		dst = kmap_page_local(last_highmem_page);
 		copy_page(dst, buffer);
-		kunmap_atomic(dst);
+		kunmap_local(dst);
 		last_highmem_page = NULL;
 	}
 }
@@ -2881,13 +2881,13 @@ static inline void swap_two_pages_data(struct page *p1, struct page *p2,
 {
 	void *kaddr1, *kaddr2;
 
-	kaddr1 = kmap_atomic(p1);
-	kaddr2 = kmap_atomic(p2);
+	kaddr1 = kmap_local_page(p1);
+	kaddr2 = kmap_local_page(p2);
 	copy_page(buf, kaddr1);
 	copy_page(kaddr1, kaddr2);
 	copy_page(kaddr2, buf);
-	kunmap_atomic(kaddr2);
-	kunmap_atomic(kaddr1);
+	kunmap_local(kaddr2);
+	kunmap_local(kaddr1);
 }
 
 /**