[RFC][PATCH 1/7] 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.

---

 b/arch/x86/include/asm/mmu.h |    1 +
 b/arch/x86/include/asm/mpx.h |    6 ++++++
 2 files changed, 7 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	2017-02-01 15:12:15.699124140 -0800
+++ b/arch/x86/include/asm/mmu.h	2017-02-01 15:12:15.702124275 -0800
@@ -34,6 +34,7 @@ typedef struct {
 #ifdef CONFIG_X86_INTEL_MPX
 	/* address of the bounds directory */
 	void __user *bd_addr;
+	int mpx_bd_shift;
 #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	2017-02-01 15:12:15.700124185 -0800
+++ b/arch/x86/include/asm/mpx.h	2017-02-01 15:12:15.702124275 -0800
@@ -68,6 +68,12 @@ 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
+	 * the old bounds directory size.  This corresponds to
+	 * what the specs call MAWA=0.
+	 */
+	mm->context.mpx_bd_shift = 0;
 }
 void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 		      unsigned long start, unsigned long end);
_