x86/fpu: Rework XSTATE_* macros to remove magic '2'

The 'xstate.c' code has a bunch of references to '2'.  This
is because we have a lot more work to do for the "extended"
xstates than the "legacy" ones and state component 2 is the
first "extended" state.

This patch replaces all of the instances of '2' with
FIRST_EXTENDED_XFEATURE, which clearly explains what is
going on.

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/20150902233128.A8C0BF51@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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

@@ -126,6 +126,8 @@ enum xfeature {
 					 | XFEATURE_MASK_ZMM_Hi256 \
 					 | XFEATURE_MASK_Hi16_ZMM)
 
+#define FIRST_EXTENDED_XFEATURE	XFEATURE_YMM
+
 /*
  * There are 16x 256-bit AVX registers named YMM0-YMM15.
  * The low 128 bits are aliased to the 16 SSE registers (XMM0-XMM15)

arch/x86/kernel/fpu/xstate.c

@@ -200,7 +200,7 @@ static void __init setup_xstate_features(void)
 
 	xfeatures_nr = fls64(xfeatures_mask);
 
-	for (leaf = 2; leaf < xfeatures_nr; leaf++) {
+	for (leaf = FIRST_EXTENDED_XFEATURE; leaf < xfeatures_nr; leaf++) {
 		cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);
 
 		xstate_offsets[leaf] = ebx;
@@ -252,7 +252,7 @@ static void __init setup_xstate_comp(void)
 	xstate_comp_offsets[1] = offsetof(struct fxregs_state, xmm_space);
 
 	if (!cpu_has_xsaves) {
-		for (i = 2; i < xfeatures_nr; i++) {
+		for (i = FIRST_EXTENDED_XFEATURE; i < xfeatures_nr; i++) {
 			if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
 				xstate_comp_offsets[i] = xstate_offsets[i];
 				xstate_comp_sizes[i] = xstate_sizes[i];
@@ -261,15 +261,16 @@ static void __init setup_xstate_comp(void)
 		return;
 	}
 
-	xstate_comp_offsets[2] = FXSAVE_SIZE + XSAVE_HDR_SIZE;
+	xstate_comp_offsets[FIRST_EXTENDED_XFEATURE] =
+		FXSAVE_SIZE + XSAVE_HDR_SIZE;
 
-	for (i = 2; i < xfeatures_nr; i++) {
+	for (i = FIRST_EXTENDED_XFEATURE; i < xfeatures_nr; i++) {
 		if (test_bit(i, (unsigned long *)&xfeatures_mask))
 			xstate_comp_sizes[i] = xstate_sizes[i];
 		else
 			xstate_comp_sizes[i] = 0;
 
-		if (i > 2)
+		if (i > FIRST_EXTENDED_XFEATURE)
 			xstate_comp_offsets[i] = xstate_comp_offsets[i-1]
 					+ xstate_comp_sizes[i-1];
 
@@ -325,7 +326,7 @@ static unsigned int __init calculate_xstate_size(void)
 	}
 
 	calculated_xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
-	for (i = 2; i < 64; i++) {
+	for (i = FIRST_EXTENDED_XFEATURE; i < 64; i++) {
 		if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
 			cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
 			calculated_xstate_size += eax;