linux-kernel - [PATCH 05/11] x86, fpu: add helper xfeature_nr_enabled() instead of test

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Message-Id: <20150827171107.219DA1AA@viggo.jf.intel.com>
Date:	Thu, 27 Aug 2015 10:11:07 -0700
From:	Dave Hansen <dave@...1.net>
To:	dave@...1.net
Cc:	dave.hansen@...ux.intel.com, mingo@...hat.com, x86@...nel.org,
	bp@...en8.de, fenghua.yu@...el.com, tim.c.chen@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH 05/11] x86, fpu: add helper xfeature_nr_enabled() instead of test_bit()


From: Dave Hansen <dave.hansen@...ux.intel.com>

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_nr_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@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: x86@...nel.org
Cc: Borislav Petkov <bp@...en8.de>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org
---

 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	2015-08-27 10:08:02.716686431 -0700
+++ b/arch/x86/kernel/fpu/xstate.c	2015-08-27 10:08:02.720686613 -0700
@@ -207,6 +207,16 @@ 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_nr_enabled(enum xfeature_nr xfeature_nr)
+{
+	return !!(xfeatures_mask & (1UL << xfeature_nr));
+}
+
+/*
  * 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.
@@ -226,7 +236,7 @@ static void __init setup_xstate_comp(voi
 
 	if (!cpu_has_xsaves) {
 		for (i = FIRST_EXTENDED_XFEATURE_NR; i < XFEATURES_NR_MAX; i++) {
-			if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
+			if (xfeature_nr_enabled(i)) {
 				xstate_comp_offsets[i] = xstate_offsets[i];
 				xstate_comp_sizes[i] = xstate_sizes[i];
 			}
@@ -238,7 +248,7 @@ static void __init setup_xstate_comp(voi
 	  	FXSAVE_SIZE + XSAVE_HDR_SIZE;
 
 	for (i = FIRST_EXTENDED_XFEATURE_NR; i < XFEATURES_NR_MAX; i++) {
-		if (test_bit(i, (unsigned long *)&xfeatures_mask))
+		if (xfeature_nr_enabled(i))
 			xstate_comp_sizes[i] = xstate_sizes[i];
 		else
 			xstate_comp_sizes[i] = 0;
@@ -299,7 +309,7 @@ static void __init init_xstate_size(void
 
 	xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE;
 	for (i = FIRST_EXTENDED_XFEATURE_NR; i < 64; i++) {
-		if (test_bit(i, (unsigned long *)&xfeatures_mask)) {
+		if (xfeature_nr_enabled(i)) {
 			cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
 			xstate_size += eax;
 		}
_
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