On Fri, Feb 17, 2017 at 9:19 AM, Dave Hansen [off-list ref] wrote:

On 02/17/2017 06:13 AM, Kirill A. Shutemov wrote:

quoted

+/*
+ * Default maximum virtual address. This is required for
+ * compatibility with applications that assumes 47-bit VA.
+ * The limit can be changed with prctl(PR_SET_MAX_VADDR).
+ */
+#define MAX_VADDR_DEFAULT    ((1UL << 47) - PAGE_SIZE)

This is a bit goofy.  It's not the largest virtual adddress that can be
accessed, but the beginning of the last page.

No, it really is the limit.  We don't allow user code to map the last
page because ti would be a root hole due to SYSRET.  Thanks, Intel.
See the comment near TASK_SIZE_MAX IIRC.

--Andy