x86/fpu: Clean up xstate feature reservation

Put MPX support into its separate high level structure, and
also replace the fixed YMM, LWP and MPX structures in
xregs_state with just reservations - their exact offsets
in the structure will depend on the CPU and no code actually
relies on those fields.

No change in functionality.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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

@@ -145,12 +145,21 @@ struct bndcsr {
 	u64				bndstatus;
 } __packed;
 
+struct mpx_struct {
+	struct bndreg			bndreg[4];
+	struct bndcsr			bndcsr;
+};
+
 struct xstate_header {
 	u64				xfeatures;
 	u64				xcomp_bv;
 	u64				reserved[6];
 } __attribute__((packed));
 
+/* New processor state extensions should be added here: */
+#define XSTATE_RESERVE			(sizeof(struct ymmh_struct) + \
+					 sizeof(struct lwp_struct)  + \
+					 sizeof(struct mpx_struct)  )
 /*
  * This is our most modern FPU state format, as saved by the XSAVE
  * and restored by the XRSTOR instructions.
@@ -162,11 +171,7 @@ struct xstate_header {
 struct xregs_state {
 	struct fxregs_state		i387;
 	struct xstate_header		header;
-	struct ymmh_struct		ymmh;
-	struct lwp_struct		lwp;
-	struct bndreg			bndreg[4];
-	struct bndcsr			bndcsr;
-	/* New processor state extensions will go here. */
+	u8				__reserved[XSTATE_RESERVE];
 } __attribute__ ((packed, aligned (64)));
 
 /*