x86/fpu: Add xfeature_enabled() helper instead of test_bit()

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@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.B1534F86@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 3 deletions

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 61ec60bcbb63..ba6b6e0baf88 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -226,6 +226,16 @@ static void __init print_xstate_features(void)
 }
 
 /*
+ * 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(void)
 
         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(void)
                 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_xstate_size(void)
 
         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;
                 }