Let me make sure I'm grokking what you're trying to do here.

On 02/20/2017 05:15 AM, Kirill A. Shutemov wrote:

+/* MPX cannot handle addresses above 47-bits yet. */
+unsigned long mpx_unmapped_area_check(unsigned long addr, unsigned long len,
+		unsigned long flags)
+{
+	if (!kernel_managing_mpx_tables(current->mm))
+		return addr;
+	if (addr + len <= DEFAULT_MAP_WINDOW)
+		return addr;

At this point, we know MPX management is on and the hint is for memory
above DEFAULT_MAP_WINDOW?

+	if (flags & MAP_FIXED)
+		return -ENOMEM;

... and if it's a MAP_FIXED request, fail it.

+	if (len > DEFAULT_MAP_WINDOW)
+		return -ENOMEM;

What is this case for?  If addr+len wraps?

+	/* Look for unmap area within DEFAULT_MAP_WINDOW */
+	return 0;
+}

Otherwise, blow away the hint, which we know is high and needs to
be discarded?

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