Commit aa969515 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Herbert Xu
Browse files

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: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent b517b0fb

crypto/ahash.c

+2 −2
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ static int hash_walk_next(struct crypto_hash_walk *walk) 
	unsigned int nbytes = min(walk->entrylen,

				  ((unsigned int)(PAGE_SIZE)) - offset);



	walk->data = kmap_atomic(walk->pg);

	walk->data = kmap_local_page(walk->pg);

	walk->data += offset;



	if (offset & alignmask) {
@@ -95,7 +95,7 @@ int crypto_hash_walk_done(struct crypto_hash_walk *walk, int err) 
		}

	}



	kunmap_atomic(walk->data);

	kunmap_local(walk->data);

	crypto_yield(walk->flags);



	if (err)

crypto/shash.c

+2 −2
Original line number Diff line number Diff line
@@ -320,10 +320,10 @@ int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc) 
	     nbytes <= min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset))) {

		void *data;



		data = kmap_atomic(sg_page(sg));

		data = kmap_local_page(sg_page(sg));

		err = crypto_shash_digest(desc, data + offset, nbytes,

					  req->result);

		kunmap_atomic(data);

		kunmap_local(data);

	} else

		err = crypto_shash_init(desc) ?:

		      shash_ahash_finup(req, desc);

include/crypto/scatterwalk.h

+2 −2
Original line number Diff line number Diff line
@@ -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);

}