fs/ecryptfs: Use kmap_local_page() in ecryptfs_write()

kmap_atomic() is deprecated in favor of kmap_local_page().

Therefore, replace kmap_atomic() with kmap_local_page() in
ecryptfs_write().

kmap_atomic() is implemented like kmap_local_page() which also disables
page-faults and preemption (the latter only for !PREEMPT_RT kernels).

The code within the mapping/un-mapping in ecryptfs_write() does not
depend on the above-mentioned side effects so that a mere replacement 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()).

Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
HIGHMEM64GB enabled.
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Message-Id: <20230426172223.8896-3-fmdefrancesco@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/ecryptfs/read_write.c

@@ -140,7 +140,7 @@ int ecryptfs_write(struct inode *ecryptfs_inode, char *data, loff_t offset,
 			       ecryptfs_page_idx, rc);
 			goto out;
 		}
-		ecryptfs_page_virt = kmap_atomic(ecryptfs_page);
+		ecryptfs_page_virt = kmap_local_page(ecryptfs_page);
 
 		/*
 		 * pos: where we're now writing, offset: where the request was
@@ -163,7 +163,7 @@ int ecryptfs_write(struct inode *ecryptfs_inode, char *data, loff_t offset,
 			       (data + data_offset), num_bytes);
 			data_offset += num_bytes;
 		}
-		kunmap_atomic(ecryptfs_page_virt);
+		kunmap_local(ecryptfs_page_virt);
 		flush_dcache_page(ecryptfs_page);
 		SetPageUptodate(ecryptfs_page);
 		unlock_page(ecryptfs_page);