sched/preempt, powerpc: Disable preemption in enable_kernel_altivec() explicitly

enable_kernel_altivec() has to be called with disabled preemption.
Let's make this explicit, to prepare for pagefault_disable() not
touching preemption anymore.

Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-14-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/crypto/vmx/aes_cbc.c

@@ -79,11 +79,13 @@ static int p8_aes_cbc_setkey(struct crypto_tfm *tfm, const u8 *key,
     int ret;
     struct p8_aes_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
 
+    preempt_disable();
     pagefault_disable();
     enable_kernel_altivec();
     ret = aes_p8_set_encrypt_key(key, keylen * 8, &ctx->enc_key);
     ret += aes_p8_set_decrypt_key(key, keylen * 8, &ctx->dec_key);
     pagefault_enable();
+    preempt_enable();
 
     ret += crypto_blkcipher_setkey(ctx->fallback, key, keylen);
     return ret;
@@ -106,6 +108,7 @@ static int p8_aes_cbc_encrypt(struct blkcipher_desc *desc,
     if (in_interrupt()) {
         ret = crypto_blkcipher_encrypt(&fallback_desc, dst, src, nbytes);
     } else {
+	preempt_disable();
         pagefault_disable();
         enable_kernel_altivec();
 
@@ -119,6 +122,7 @@ static int p8_aes_cbc_encrypt(struct blkcipher_desc *desc,
 	}
 
         pagefault_enable();
+	preempt_enable();
     }
 
     return ret;
@@ -141,6 +145,7 @@ static int p8_aes_cbc_decrypt(struct blkcipher_desc *desc,
     if (in_interrupt()) {
         ret = crypto_blkcipher_decrypt(&fallback_desc, dst, src, nbytes);
     } else {
+	preempt_disable();
         pagefault_disable();
         enable_kernel_altivec();
 
@@ -154,6 +159,7 @@ static int p8_aes_cbc_decrypt(struct blkcipher_desc *desc,
 		}
 
         pagefault_enable();
+	preempt_enable();
     }
 
     return ret;