Documentation: Add powerpc options for spec_store_bypass_disable

Document the support for spec_store_bypass_disable that was added for
powerpc in commit a048a07d7f45 ("powerpc/64s: Add support for a store
forwarding barrier at kernel entry/exit").

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 533ff5c..4bb6004 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4060,6 +4060,8 @@
                        This parameter controls whether the Speculative Store
                        Bypass optimization is used.
 
+                       On x86 the options are:
+
                        on      - Unconditionally disable Speculative Store Bypass
                        off     - Unconditionally enable Speculative Store Bypass
                        auto    - Kernel detects whether the CPU model contains an
@@ -4075,12 +4077,20 @@
                        seccomp - Same as "prctl" above, but all seccomp threads
                                  will disable SSB unless they explicitly opt out.
 
-                       Not specifying this option is equivalent to
-                       spec_store_bypass_disable=auto.
-
                        Default mitigations:
                        X86:    If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
 
+                       On powerpc the options are:
+
+                       on,auto - On Power8 and Power9 insert a store-forwarding
+                                 barrier on kernel entry and exit. On Power7
+                                 perform a software flush on kernel entry and
+                                 exit.
+                       off     - No action.
+
+                       Not specifying this option is equivalent to
+                       spec_store_bypass_disable=auto.
+
        spia_io_base=   [HW,MTD]
        spia_fio_base=
        spia_pedr=