x86/fpu/mpx: Rework MPX 'xstate' types

MPX includes two separate "extended state components". There is
no real need to have an 'mpx_struct' because we never really
manage the states together.

We also separate out the actual data in 'mpx_bndcsr_state' from
the padding. We will shortly be checking the state sizes
against our structures and need them to match. For consistency,
we also ensure to prefix these types with 'mpx_'.

Lastly, we add some comments to mirror some of the descriptions
in the Intel documents (SDM) of the various state components.

Signed-off-by: Dave Hansen <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: Fenghua Yu <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Tim Chen <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

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

···
 };
 
 /* Intel MPX support: */
-struct bndreg {
+
+struct mpx_bndreg {
 	u64				lower_bound;
 	u64				upper_bound;
 } __packed;
+/*
+ * State component 3 is used for the 4 128-bit bounds registers
+ */
+struct mpx_bndreg_state {
+	struct mpx_bndreg		bndreg[4];
+} __packed;
 
-struct bndcsr {
+/*
+ * State component 4 is used for the 64-bit user-mode MPX
+ * configuration register BNDCFGU and the 64-bit MPX status
+ * register BNDSTATUS.  We call the pair "BNDCSR".
+ */
+struct mpx_bndcsr {
 	u64				bndcfgu;
 	u64				bndstatus;
 } __packed;
 
-struct mpx_struct {
-	struct bndreg			bndreg[4];
-	struct bndcsr			bndcsr;
-};
+/*
+ * The BNDCSR state is padded out to be 64-bytes in size.
+ */
+struct mpx_bndcsr_state {
+	union {
+		struct mpx_bndcsr		bndcsr;
+		u8				pad_to_64_bytes[64];
+	};
+} __packed;
 
 struct xstate_header {
 	u64				xfeatures;

arch/x86/include/asm/trace/mpx.h

···
 TRACE_EVENT(mpx_bounds_register_exception,
 
 	TP_PROTO(void *addr_referenced,
-		 const struct bndreg *bndreg),
+		 const struct mpx_bndreg *bndreg),
 	TP_ARGS(addr_referenced, bndreg),
 
 	TP_STRUCT__entry(
···
 
 TRACE_EVENT(bounds_exception_mpx,
 
-	TP_PROTO(const struct bndcsr *bndcsr),
+	TP_PROTO(const struct mpx_bndcsr *bndcsr),
 	TP_ARGS(bndcsr),
 
 	TP_STRUCT__entry(
···
 /*
  * This gets used outside of MPX-specific code, so we need a stub.
  */
-static inline void trace_bounds_exception_mpx(const struct bndcsr *bndcsr)
+static inline
+void trace_bounds_exception_mpx(const struct mpx_bndcsr *bndcsr)
 {
 }
 

arch/x86/kernel/traps.c

···
 
 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 {
-	const struct bndcsr *bndcsr;
+	const struct mpx_bndcsr *bndcsr;
 	siginfo_t *info;
 
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");

arch/x86/mm/mpx.c

···
  */
 siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
 {
-	const struct bndreg *bndregs, *bndreg;
+	const struct mpx_bndreg_state *bndregs;
+	const struct mpx_bndreg *bndreg;
 	siginfo_t *info = NULL;
 	struct insn insn;
 	uint8_t bndregno;
···
 		goto err_out;
 	}
 	/* now go select the individual register in the set of 4 */
-	bndreg = &bndregs[bndregno];
+	bndreg = &bndregs->bndreg[bndregno];
 
 	info = kzalloc(sizeof(*info), GFP_KERNEL);
 	if (!info) {
···
 
 static __user void *mpx_get_bounds_dir(void)
 {
-	const struct bndcsr *bndcsr;
+	const struct mpx_bndcsr *bndcsr;
 
 	if (!cpu_feature_enabled(X86_FEATURE_MPX))
 		return MPX_INVALID_BOUNDS_DIR;
···
 static int do_mpx_bt_fault(void)
 {
 	unsigned long bd_entry, bd_base;
-	const struct bndcsr *bndcsr;
+	const struct mpx_bndcsr *bndcsr;
 	struct mm_struct *mm = current->mm;
 
 	bndcsr = get_xsave_field_ptr(XFEATURE_MASK_BNDCSR);