crypto: scatterwalk - use kmap_local() not kmap_atomic()

kmap_atomic() is used to create short-lived mappings of pages that may
not be accessible via the kernel direct map. This is only needed on
32-bit architectures that implement CONFIG_HIGHMEM, but it can be used
on 64-bit other architectures too, where the returned mapping is simply
the kernel direct address of the page.

However, kmap_atomic() does not support migration on CONFIG_HIGHMEM
configurations, due to the use of per-CPU kmap slots, and so it disables
preemption on all architectures, not just the 32-bit ones. This implies
that all scatterwalk based crypto routines essentially execute with
preemption disabled all the time, which is less than ideal.

So let's switch scatterwalk_map/_unmap and the shash/ahash routines to
kmap_local() instead, which serves a similar purpose, but without the
resulting impact on preemption on architectures that have no need for
CONFIG_HIGHMEM.

Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "Elliott, Robert (Servers)" <elliott@hpe.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/crypto/scatterwalk.h b/include/crypto/scatterwalk.h
index f2c42b4111b1..32fc4473175b 100644
--- a/include/crypto/scatterwalk.h
+++ b/include/crypto/scatterwalk.h
@@ -53,7 +53,7 @@ static inline struct page *scatterwalk_page(struct scatter_walk *walk)
 
 static inline void scatterwalk_unmap(void *vaddr)
 {
-	kunmap_atomic(vaddr);
+	kunmap_local(vaddr);
 }
 
 static inline void scatterwalk_start(struct scatter_walk *walk,
@@ -65,7 +65,7 @@ static inline void scatterwalk_start(struct scatter_walk *walk,
 
 static inline void *scatterwalk_map(struct scatter_walk *walk)
 {
-	return kmap_atomic(scatterwalk_page(walk)) +
+	return kmap_local_page(scatterwalk_page(walk)) +
 	       offset_in_page(walk->offset);
 }