[PATCH] pm: Replace deprecated kmap_atomic() with kmap_local_page()

[PATCH] pm: Replace deprecated kmap_atomic() with kmap_local_page()

[David Reaver]

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@davidreaver.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);
 }
 
 /**

Re: [PATCH] pm: Replace deprecated kmap_atomic() with kmap_local_page()

[kernel test robot]

Hi David,

kernel test robot noticed the following build warnings:

[auto build test WARNING on amd-pstate/linux-next]
[also build test WARNING on amd-pstate/bleeding-edge linus/master v6.13-rc6 next-20250110]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/David-Reaver/pm-Replace-deprecated-kmap_atomic-with-kmap_local_page/20250112-100253
base:   https://git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git linux-next
patch link:    https://lore.kernel.org/r/20250112015535.191527-1-me%40davidreaver.com
patch subject: [PATCH] pm: Replace deprecated kmap_atomic() with kmap_local_page()
config: i386-buildonly-randconfig-005-20250112 (https://download.01.org/0day-ci/archive/20250112/202501122002.vD4o8M9T-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250112/202501122002.vD4o8M9T-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202501122002.vD4o8M9T-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/power/snapshot.c: In function 'copy_last_highmem_page':
   kernel/power/snapshot.c:2567:23: error: implicit declaration of function 'kmap_page_local' [-Werror=implicit-function-declaration]
    2567 |                 dst = kmap_page_local(last_highmem_page);
         |                       ^~~~~~~~~~~~~~~
>> kernel/power/snapshot.c:2567:21: warning: assignment to 'void *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
    2567 |                 dst = kmap_page_local(last_highmem_page);
         |                     ^
   cc1: some warnings being treated as errors


vim +2567 kernel/power/snapshot.c

  2554	
  2555	/**
  2556	 * copy_last_highmem_page - Copy most the most recent highmem image page.
  2557	 *
  2558	 * Copy the contents of a highmem image from @buffer, where the caller of
  2559	 * snapshot_write_next() has stored them, to the right location represented by
  2560	 * @last_highmem_page .
  2561	 */
  2562	static void copy_last_highmem_page(void)
  2563	{
  2564		if (last_highmem_page) {
  2565			void *dst;
  2566	
> 2567			dst = kmap_page_local(last_highmem_page);
  2568			copy_page(dst, buffer);
  2569			kunmap_local(dst);
  2570			last_highmem_page = NULL;
  2571		}
  2572	}
  2573	

-- 
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https://github.com/intel/lkp-tests/wiki