[PATCH 3/6] crypto: x86/chacha20 - limit the preemption-disabled section

[Eric Biggers]

From: Eric Biggers <ebiggers@xxxxxxxxxx>

To improve responsiveness, disable preemption for each step of the walk
(which is at most PAGE_SIZE) rather than for the entire
encryption/decryption operation.

Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
 arch/x86/crypto/chacha20_glue.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/crypto/chacha20_glue.c b/arch/x86/crypto/chacha20_glue.c
index 1e9e665092264..5928fee7acdd4 100644
--- a/arch/x86/crypto/chacha20_glue.c
+++ b/arch/x86/crypto/chacha20_glue.c
@@ -100,26 +100,24 @@ static int chacha20_simd(struct skcipher_request *req)
 	if (req->cryptlen <= CHACHA_BLOCK_SIZE || !may_use_simd())
 		return crypto_chacha_crypt(req);
 
-	err = skcipher_walk_virt(&walk, req, true);
+	err = skcipher_walk_virt(&walk, req, false);
 
 	crypto_chacha_init(state, ctx, walk.iv);
 
-	kernel_fpu_begin();
-
 	while (walk.nbytes > 0) {
 		unsigned int nbytes = walk.nbytes;
 
 		if (nbytes < walk.total)
 			nbytes = round_down(nbytes, walk.stride);
 
+		kernel_fpu_begin();
 		chacha20_dosimd(state, walk.dst.virt.addr, walk.src.virt.addr,
 				nbytes);
+		kernel_fpu_end();
 
 		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
 	}
 
-	kernel_fpu_end();
-
 	return err;
 }
 
-- 
2.19.2