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-rw-r--r--Documentation/spec_ctrl.txt34
1 files changed, 21 insertions, 13 deletions
diff --git a/Documentation/spec_ctrl.txt b/Documentation/spec_ctrl.txt
index ddbebcd01208..1b3690d30943 100644
--- a/Documentation/spec_ctrl.txt
+++ b/Documentation/spec_ctrl.txt
@@ -25,19 +25,21 @@ PR_GET_SPECULATION_CTRL
-----------------------
PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
-which is selected with arg2 of prctl(2). The return value uses bits 0-2 with
+which is selected with arg2 of prctl(2). The return value uses bits 0-3 with
the following meaning:
-==== ================ ===================================================
-Bit Define Description
-==== ================ ===================================================
-0 PR_SPEC_PRCTL Mitigation can be controlled per task by
- PR_SET_SPECULATION_CTRL
-1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
- disabled
-2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
- enabled
-==== ================ ===================================================
+==== ===================== ===================================================
+Bit Define Description
+==== ===================== ===================================================
+0 PR_SPEC_PRCTL Mitigation can be controlled per task by
+ PR_SET_SPECULATION_CTRL
+1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
+ disabled
+2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
+ enabled
+3 PR_SPEC_FORCE_DISABLE Same as PR_SPEC_DISABLE, but cannot be undone. A
+ subsequent prctl(..., PR_SPEC_ENABLE) will fail.
+==== ===================== ===================================================
If all bits are 0 the CPU is not affected by the speculation misfeature.
@@ -47,9 +49,11 @@ misfeature will fail.
PR_SET_SPECULATION_CTRL
-----------------------
+
PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which
is selected by arg2 of :manpage:`prctl(2)` per task. arg3 is used to hand
-in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE.
+in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE or
+PR_SPEC_FORCE_DISABLE.
Common error codes
------------------
@@ -70,10 +74,13 @@ Value Meaning
0 Success
ERANGE arg3 is incorrect, i.e. it's neither PR_SPEC_ENABLE nor
- PR_SPEC_DISABLE
+ PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE
ENXIO Control of the selected speculation misfeature is not possible.
See PR_GET_SPECULATION_CTRL.
+
+EPERM Speculation was disabled with PR_SPEC_FORCE_DISABLE and caller
+ tried to enable it again.
======= =================================================================
Speculation misfeature controls
@@ -84,3 +91,4 @@ Speculation misfeature controls
* prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, 0, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
* prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
+ * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);