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

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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>
This commit is contained in:
Ard Biesheuvel 2022-12-13 17:13:10 +01:00 committed by Herbert Xu
parent b517b0fbfe
commit aa9695157f
3 changed files with 6 additions and 6 deletions
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4
crypto/ahash.c
View file

@ -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)

4
crypto/shash.c
View file

@ -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);

4
include/crypto/scatterwalk.h
View file

@ -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);
}