[PATCH] fs: Call kmap_local_page() in copy_string_kernel()

From: Fabio M. De Francesco
Date: Sun Jul 10 2022 - 06:02:06 EST

The use of kmap_atomic() is being deprecated in favor of kmap_local_page().

With kmap_local_page(), the mappings are per thread, CPU local, not
globally visible and can take page faults. Furthermore, the mappings can be
acquired from any context (including interrupts).

Therefore, use kmap_local_page() in copy_string_kernel() instead of

Tested with xfstests on a QEMU + KVM 32-bits VM booting a kernel with
HIGHMEM64GB enabled.

Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>

I sent a first patch to fs/exec.c for converting kmap() and kmap_atomic()
to kmap_local_page():

Some days ago, Ira Weiny, while he was reviewing that patch, made me notice
that I had overlooked a second kmap_atomic() in the same file (thanks):

I've been asked to send this as an additional change. This is why there will
not be any second version of that previous patch.

fs/exec.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 4a2129c0d422..5fa652ca5823 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -639,11 +639,11 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
page = get_arg_page(bprm, pos, 1);
if (!page)
return -E2BIG;
- kaddr = kmap_atomic(page);
+ kaddr = kmap_local_page(page);
flush_arg_page(bprm, pos & PAGE_MASK, page);
memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
- kunmap_atomic(kaddr);
+ kunmap_local(kaddr);