x86/fpu: Rework YMM definition

We are about to rework all of the "extended state" definitions.
This makes the 'ymm' naming consistent with the AVX-512 types
we will introduce later.

We also add a convenience type: "reg_128_bit" so that we do
not have to spell out our arithmetic.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: dave@sr71.net
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20150902233129.B4EB045F@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/fpu/types.h

@@ -128,17 +128,23 @@ enum xfeature {
 
 #define FIRST_EXTENDED_XFEATURE	XFEATURE_YMM
 
+struct reg_128_bit {
+	u8      regbytes[128/8];
+};
+
 /*
+ * State component 2:
+ *
  * There are 16x 256-bit AVX registers named YMM0-YMM15.
  * The low 128 bits are aliased to the 16 SSE registers (XMM0-XMM15)
- * and are stored in 'struct fxregs_state::xmm_space[]'.
+ * and are stored in 'struct fxregs_state::xmm_space[]' in the
+ * "legacy" area.
  *
- * The high 128 bits are stored here:
- *    16x 128 bits == 256 bytes.
+ * The high 128 bits are stored here.
  */
 struct ymmh_struct {
-	u8				ymmh_space[256];
-};
+	struct reg_128_bit              hi_ymm[16];
+} __packed;
 
 /* Intel MPX support: */