[PATCH 09/15] x86, fpu: add helper xfeature_enabled() instead of test_bit()

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

We currently use test_bit() in a few places to see if an xfeature
is enabled.  It ends up being a bit ugly because 'xfeatures_mask'
is a u64 and test_bit wants an 'unsigned long' so it requires a
cast.  The *_bit() functions are also techincally atomic, which
we have no need for here.

So, remove the test_bit()s and replace with the new
xfeature_enabled() helper.

This also provides a central place to add a comment about the
future need to support 'system xstates'.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---

 b/arch/x86/kernel/fpu/xstate.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff -puN arch/x86/kernel/fpu/xstate.c~use-xfeature_enabled arch/x86/kernel/fpu/xstate.c
--- a/arch/x86/kernel/fpu/xstate.c~use-xfeature_enabled	2015-08-31 15:17:35.008910377 -0700
+++ b/arch/x86/kernel/fpu/xstate.c	2015-08-31 15:17:35.011910514 -0700
@@ -226,6 +226,16 @@ static void __init print_xstate_features
 }
 
 /*
+ * Note that in the future we will likely need a pair of
+ * functions here: one for user xstates and the other for
+ * system xstates.  For now, they are the same.
+ */
+static int xfeature_enabled(enum xfeature xfeature)
+{
+	return !!(xfeatures_mask & (1UL << xfeature));
+}
+
+/*
  * This function sets up offsets and sizes of all extended states in
  * xsave area. This supports both standard format and compacted format
  * of the xsave aread.
@@ -245,7 +255,7 @@ static void __init setup_xstate_comp(voi
 
 	if (!cpu_has_xsaves) {
 		for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) {
-			if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
+			if (xfeature_enabled(i)) {
 				xstate_comp_offsets[i] = xstate_offsets[i];
 				xstate_comp_sizes[i] = xstate_sizes[i];
 			}
@@ -257,7 +267,7 @@ static void __init setup_xstate_comp(voi
 	  	FXSAVE_SIZE + XSAVE_HDR_SIZE;
 
 	for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) {
-		if (test_bit(i, (unsigned long *)&xfeatures_mask))
+		if (xfeature_enabled(i))
 			xstate_comp_sizes[i] = xstate_sizes[i];
 		else
 			xstate_comp_sizes[i] = 0;
@@ -319,7 +329,7 @@ static unsigned int __init calculate_xst
 
 	calculated_xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
 	for (i = FIRST_EXTENDED_XFEATURE; i < 64; i++) {
-		if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
+		if (xfeature_enabled(i)) {
 			cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
 			calculated_xstate_size += eax;
 		}
_
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