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Subject[RFC][PATCH 1/7] x86, mpx: introduce per-mm MPX table size tracking
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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);
_
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