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 <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/20150902233129.384B73EB@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

4 files changed, 33 insertions, 14 deletions

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 9f579305dd11..4d8c2009b94e 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -141,20 +141,37 @@ struct ymmh_struct {
 };
 
 /* 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;
diff --git a/arch/x86/include/asm/trace/mpx.h b/arch/x86/include/asm/trace/mpx.h
index 173dd3ba108c..0f492fc50bce 100644
--- a/arch/x86/include/asm/trace/mpx.h
+++ b/arch/x86/include/asm/trace/mpx.h
@@ -11,7 +11,7 @@
 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(
@@ -44,7 +44,7 @@ TRACE_EVENT(mpx_bounds_register_exception,
 
 TRACE_EVENT(bounds_exception_mpx,
 
-        TP_PROTO(const struct bndcsr *bndcsr),
+        TP_PROTO(const struct mpx_bndcsr *bndcsr),
         TP_ARGS(bndcsr),
 
         TP_STRUCT__entry(
@@ -116,7 +116,8 @@ TRACE_EVENT(mpx_new_bounds_table,
 /*
  * 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)
 {
 }
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 0cd2ac5c0f28..ade185a46b1d 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -361,7 +361,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 
 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");
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index f35fc9c6ed50..b0ae85f90f10 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -237,7 +237,8 @@ bad_opcode:
  */
 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;
@@ -264,7 +265,7 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
                 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) {
@@ -306,7 +307,7 @@ err_out:
 
 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;
@@ -489,7 +490,7 @@ out_unmap:
 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);