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| author | Brendan Jackman <jackmanb@google.com> | 2025-10-15 17:02:05 +0000 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2025-10-29 16:19:27 -0600 |
| commit | aab703b3c6f62f698d294444abe05cc83b50cff2 (patch) | |
| tree | ca4532edaec33ab673cd49e4b3883a67e96fe5d1 | |
| parent | ba2457109d5b47a90fe565b39524f7225fc23e60 (diff) | |
Documentation: clarify PR_SPEC_L1D_FLUSH
For PR_SPEC_STORE_BYPASS and PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE
means "disable the speculation bug" i.e. "enable the mitigation".
For PR_SPEC_L1D_FLUSH, PR_SPEC_DISABLE means "disable the mitigation".
This is not obvious, so document it.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251015-l1d-flush-doc-v1-1-f8cefea3f2f2@google.com>
| -rw-r--r-- | Documentation/userspace-api/spec_ctrl.rst | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/Documentation/userspace-api/spec_ctrl.rst b/Documentation/userspace-api/spec_ctrl.rst index 5e8ed9eef9aa..ca89151fc0a8 100644 --- a/Documentation/userspace-api/spec_ctrl.rst +++ b/Documentation/userspace-api/spec_ctrl.rst @@ -26,7 +26,8 @@ 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 0-3 with -the following meaning: +the following meaning (with the caveat that PR_SPEC_L1D_FLUSH has less obvious +semantics, see documentation for that specific control below): ==== ====================== ================================================== Bit Define Description @@ -110,6 +111,9 @@ Speculation misfeature controls - PR_SPEC_L1D_FLUSH: Flush L1D Cache on context switch out of the task (works only when tasks run on non SMT cores) +For this control, PR_SPEC_ENABLE means that the **mitigation** is enabled (L1D +is flushed), PR_SPEC_DISABLE means it is disabled. + Invocations: * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_L1D_FLUSH, 0, 0, 0); * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_L1D_FLUSH, PR_SPEC_ENABLE, 0, 0); |