[RFC][PATCH 1/4] x86, mpx: introduce per-mm MPX table size tracking

[Dave Hansen]

Larger address spaces mean larger MPX bounds table sizes.  This
tracks which size tables we are using.

"MAWA" is what the hardware documentation calls this feature:
MPX Address-Width Adjust.  We will carry that nomenclature throughout
this series.

The new field will be optimized and get packed into 'bd_addr' in a later
patch.  But, leave it separate for now to make the series simpler.

---

 b/arch/x86/include/asm/mmu.h |    1 +
 b/arch/x86/include/asm/mpx.h |    9 +++++++++
 2 files changed, 10 insertions(+)

diff -puN arch/x86/include/asm/mmu.h~mawa-020-mmu_context-mawa arch/x86/include/asm/mmu.h
--- a/arch/x86/include/asm/mmu.h~mawa-020-mmu_context-mawa	2017-01-26 14:31:32.643673297 -0800
+++ b/arch/x86/include/asm/mmu.h	2017-01-26 14:31:32.647673476 -0800
@@ -34,6 +34,7 @@ typedef struct {
 #ifdef CONFIG_X86_INTEL_MPX
 	/* address of the bounds directory */
 	void __user *bd_addr;
+	int mpx_mawa;
 #endif
 } mm_context_t;
 
diff -puN arch/x86/include/asm/mpx.h~mawa-020-mmu_context-mawa arch/x86/include/asm/mpx.h
--- a/arch/x86/include/asm/mpx.h~mawa-020-mmu_context-mawa	2017-01-26 14:31:32.644673342 -0800
+++ b/arch/x86/include/asm/mpx.h	2017-01-26 14:31:32.648673521 -0800
@@ -68,6 +68,15 @@ static inline void mpx_mm_init(struct mm
 	 * directory, so point this at an invalid address.
 	 */
 	mm->context.bd_addr = MPX_INVALID_BOUNDS_DIR;
+	/*
+	 * All processes start out in "legacy" MPX mode with
+	 * MAWA=0.
+	 */
+	mm->context.mpx_mawa = 0;
+}
+static inline int mpx_mawa_shift(struct mm_struct *mm)
+{
+	return mm->context.mpx_mawa;
 }
 void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 		      unsigned long start, unsigned long end);
_