diff -puN /dev/null Documentation/x86/pti.txt[...]
--- /dev/null 2017-12-15 13:48:30.454245127 -0800
+++ b/Documentation/x86/pti.txt 2018-01-04 21:38:28.826772303 -0800
@@ -0,0 +1,187 @@
+This sharing at the PGD level also inherently shares all the lower
+layers of the page tables. This leaves a single, shared set of
+userspace page tables to manage. One PTE to lock, one set set of
+accessed bits, dirty bits, etc...
+2. Allow PTI to enabled/disabled at runtime in addition to the
+ boot-time switching.