On Thu Oct 30, 2025 at 1:59 PM UTC, Brendan Jackman wrote:

-ENXIO   Control of the selected speculation misfeature is not possible.
-        See PR_GET_SPECULATION_CTRL.
+ENXIO   For PR_SPEC_STORE_BYPASS: control of the selected speculation misfeature
+        is not possible via prctl, because of the system's boot configuration.
+
+EPERM   Speculation was disabled with PR_SPEC_FORCE_DISABLE and caller tried to
+        enable it again.
+
+EPERM   For PR_SPEC_STORE_BYPASS and PR_SPEC_INDIRECT_BRANCH: control of the

Ugh,           ^^^^^^^^^^^^^^^^^^^^ that should be PR_SPEC_L1D_FLUSH

I will wait a day or two before v2 in case anyone else spots other
mistakes or has other comments.