crypto: x86/aegis - Fix sleeping when disallowed on PREEMPT_RT

skcipher_walk_done() can call kfree(), which takes a spinlock, which
makes it incorrect to call while preemption is disabled on PREEMPT_RT.
Therefore, end the kernel-mode FPU section before calling
skcipher_walk_done(), and restart it afterwards.

Moreover, pass atomic=false to skcipher_walk_aead_encrypt() instead of
atomic=true.  The point of atomic=true was to make skcipher_walk_done()
safe to call while in a kernel-mode FPU section, but that does not
actually work.  So just use the usual atomic=false.

Fixes: 1d373d4 ("crypto: x86 - Add optimized AEGIS implementations")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Author: Eric Biggers

arch/x86/crypto/aegis128-aesni-glue.c

@@ -119,7 +119,9 @@ crypto_aegis128_aesni_process_crypt(struct aegis_state *state,
 					   walk->dst.virt.addr,
 					   round_down(walk->nbytes,
 						      AEGIS128_BLOCK_SIZE));
+		kernel_fpu_end();
 		skcipher_walk_done(walk, walk->nbytes % AEGIS128_BLOCK_SIZE);
+		kernel_fpu_begin();
 	}
 
 	if (walk->nbytes) {
@@ -131,7 +133,9 @@ crypto_aegis128_aesni_process_crypt(struct aegis_state *state,
 			aegis128_aesni_dec_tail(state, walk->src.virt.addr,
 						walk->dst.virt.addr,
 						walk->nbytes);
+		kernel_fpu_end();
 		skcipher_walk_done(walk, 0);
+		kernel_fpu_begin();
 	}
 }
 
@@ -176,9 +180,9 @@ crypto_aegis128_aesni_crypt(struct aead_request *req,
 	struct aegis_state state;
 
 	if (enc)
-		skcipher_walk_aead_encrypt(&walk, req, true);
+		skcipher_walk_aead_encrypt(&walk, req, false);
 	else
-		skcipher_walk_aead_decrypt(&walk, req, true);
+		skcipher_walk_aead_decrypt(&walk, req, false);
 
 	kernel_fpu_begin();