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

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

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

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 ecryptfs_copy_up_encrypted_with_header(), the block of code between
the mapping and un-mapping does not depend on the above-mentioned side
effects of kmap_aatomic(), so that the 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()).

Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
HIGHMEM64GB enabled.

Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Message-Id: <20230426172223.8896-4-fmdefrancesco@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 373c3e5747e6a595786bfff65f88d089a1306e98..cb1e998ce54d8ff86836eb0704cdb58cfa2d5144 100644 (file)
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -125,7 +125,7 @@ ecryptfs_copy_up_encrypted_with_header(struct page *page,
                        /* This is a header extent */
                        char *page_virt;
 
-                       page_virt = kmap_atomic(page);
+                       page_virt = kmap_local_page(page);
                        memset(page_virt, 0, PAGE_SIZE);
                        /* TODO: Support more than one header extent */
                        if (view_extent_num == 0) {
@@ -138,7 +138,7 @@ ecryptfs_copy_up_encrypted_with_header(struct page *page,
                                                               crypt_stat,
                                                               &written);
                        }
-                       kunmap_atomic(page_virt);
+                       kunmap_local(page_virt);
                        flush_dcache_page(page);
                        if (rc) {
                                printk(KERN_ERR "%s: Error reading xattr "