s390/fpu: add static FPU save area for init_task

Previously, the init task did not have an allocated FPU save area and
saving an FPU state was not possible.  Now if the vector extension is
always enabled, provide a static FPU save area to save FPU states of
vector instructions that can be executed quite early.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/processor.h

@@ -139,8 +139,10 @@ struct stack_frame {
 
 #define ARCH_MIN_TASKALIGN	8
 
+extern __vector128 init_task_fpu_regs[__NUM_VXRS];
 #define INIT_THREAD {							\
 	.ksp = sizeof(init_stack) + (unsigned long) &init_stack,	\
+	.fpu.regs = (void *)&init_task_fpu_regs,			\
 }
 
 /*

arch/s390/kernel/entry.S

@@ -762,8 +762,6 @@ ENTRY(save_fpu_regs)
 	stfpc	__THREAD_FPU_fpc(%r2)
 .Lsave_fpu_regs_fpc_end:
 	lg	%r3,__THREAD_FPU_regs(%r2)
-	ltgr	%r3,%r3
-	jz	.Lsave_fpu_regs_done	  # no save area -> set CIF_FPU
 	tm	__LC_MACHINE_FLAGS+5,4	  # MACHINE_HAS_VX
 	jz	.Lsave_fpu_regs_fp	  # no -> store FP regs
 .Lsave_fpu_regs_vx_low:
@@ -1193,8 +1191,6 @@ cleanup_critical:
 	stfpc	__THREAD_FPU_fpc(%r2)
 1:	# Load register save area and check if VX is active
 	lg	%r3,__THREAD_FPU_regs(%r2)
-	ltgr	%r3,%r3
-	jz	5f			  # no save area -> set CIF_FPU
 	tm	__LC_MACHINE_FLAGS+5,4	  # MACHINE_HAS_VX
 	jz	4f			  # no VX -> store FP regs
 2:	# Store vector registers (V0-V15)

arch/s390/kernel/process.c

@@ -23,6 +23,7 @@
 #include <linux/kprobes.h>
 #include <linux/random.h>
 #include <linux/module.h>
+#include <linux/init_task.h>
 #include <asm/io.h>
 #include <asm/processor.h>
 #include <asm/vtimer.h>
@@ -36,6 +37,9 @@
 
 asmlinkage void ret_from_fork(void) asm ("ret_from_fork");
 
+/* FPU save area for the init task */
+__vector128 init_task_fpu_regs[__NUM_VXRS] __init_task_data;
+
 /*
  * Return saved PC of a blocked thread. used in kernel/sched.
  * resume in entry.S does not create a new stack frame, it