x86/speculation: Merge one test in spectre_v2_user_select_mitigation()

upstream commit a5ce9f2bb665d1d2b31f139a02dbaa2dfbb62fa6 upstream.

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
[fllinden@amazon.com: fixed contextual conflict (comment) for 5.4]
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fcc4238ee95f8427df46108118e558dec2ee482c..951eee8501bc5a49a719a2fe314ca02d0bc2d0fb 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -756,10 +756,12 @@ 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;
 
        /*
@@ -771,12 +773,6 @@ 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:
@@ -1267,7 +1263,6 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
                if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE &&
                    spectre_v2_user_stibp == SPECTRE_V2_USER_NONE)
                        return 0;
-
                /*
                 * With strict mode for both IBPB and STIBP, the instruction
                 * code paths avoid checking this task flag and instead,