x86, xsave: Support eager-only xsave features, add MPX support

Some features, like Intel MPX, work only if the kernel uses eagerfpu
model.  So we should force eagerfpu on unless the user has explicitly
disabled it.

Add definitions for Intel MPX and add it to the supported list.

[ hpa: renamed XSTATE_FLEXIBLE to XSTATE_LAZY and added comments ]

Signed-off-by: Qiaowei Ren <qiaowei.ren@intel.com>
Link: http://lkml.kernel.org/r/9E0BE1322F2F2246BD820DA9FC397ADE014A6115@SHSMSX102.ccr.corp.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/xsave.h

@@ -9,6 +9,8 @@
 #define XSTATE_FP	0x1
 #define XSTATE_SSE	0x2
 #define XSTATE_YMM	0x4
+#define XSTATE_BNDREGS	0x8
+#define XSTATE_BNDCSR	0x10
 
 #define XSTATE_FPSSE	(XSTATE_FP | XSTATE_SSE)
 
@@ -20,10 +22,14 @@
 #define XSAVE_YMM_SIZE	    256
 #define XSAVE_YMM_OFFSET    (XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET)
 
-/*
- * These are the features that the OS can handle currently.
- */
-#define XCNTXT_MASK	(XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
+/* Supported features which support lazy state saving */
+#define XSTATE_LAZY	(XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
+
+/* Supported features which require eager state saving */
+#define XSTATE_EAGER	(XSTATE_BNDREGS | XSTATE_BNDCSR)
+
+/* All currently supported features */
+#define XCNTXT_MASK	(XSTATE_LAZY | XSTATE_EAGER)
 
 #ifdef CONFIG_X86_64
 #define REX_PREFIX	"0x48, "