x86/speculation: Merge one test in spectre_v2_user_select_mitigation()

Merge the test whether the CPU supports STIBP into the test which
determines whether STIBP is required. Thus try to simplify what is
already an insane logic.

Remove a superfluous newline in a comment, while at it.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Anthony Steinhauser <asteinhauser@google.com>
Link: https://lkml.kernel.org/r/20200615065806.GB14668@zn.tnic

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0b71970d2d3d2a65848a6377d6026d9ea45929be..7beaefa9d198c08e03414509257693444c262569 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -763,10 +763,12 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
        }
 
        /*
-        * If enhanced IBRS is enabled or SMT impossible, STIBP is not
+        * If no STIBP, enhanced IBRS is enabled or SMT impossible, STIBP is not
         * required.
         */
-       if (!smt_possible || spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+       if (!boot_cpu_has(X86_FEATURE_STIBP) ||
+           !smt_possible ||
+           spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
                return;
 
        /*
@@ -778,12 +780,6 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
            boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
                mode = SPECTRE_V2_USER_STRICT_PREFERRED;
 
-       /*
-        * If STIBP is not available, clear the STIBP mode.
-        */
-       if (!boot_cpu_has(X86_FEATURE_STIBP))
-               mode = SPECTRE_V2_USER_NONE;
-
        spectre_v2_user_stibp = mode;
 
 set_mode:
@@ -1270,7 +1266,6 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
                 * Indirect branch speculation is always disabled in strict
                 * mode. It can neither be enabled if it was force-disabled
                 * by a  previous prctl call.
-
                 */
                if (spectre_v2_user_ibpb == SPECTRE_V2_USER_STRICT ||
                    spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT ||