x86/bugs: Use the cpu_smt_possible() helper instead of open-coded code

There is a helper function to check if SMT is available. Use this helper
instead of performing the check manually.

The helper function cpu_smt_possible() does exactly the same thing as
was being done manually inside spectre_v2_user_select_mitigation().
Specifically, it returns false if CONFIG_SMP is disabled, otherwise
it checks the cpu_smt_control global variable.

This change improves code consistency and reduces duplication.

No change in functionality intended.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: David Kaplan <David.Kaplan@amd.com>
Link: https://lore.kernel.org/r/20241031-x86_bugs_last_v2-v2-1-b7ff1dab840e@debian.org

arch/x86/kernel/cpu/bugs.c

@@ -1346,16 +1346,11 @@ static void __init
 spectre_v2_user_select_mitigation(void)
 {
 	enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
-	bool smt_possible = IS_ENABLED(CONFIG_SMP);
 	enum spectre_v2_user_cmd cmd;
 
 	if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
 		return;
 
-	if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
-	    cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
-		smt_possible = false;
-
 	cmd = spectre_v2_parse_user_cmdline();
 	switch (cmd) {
 	case SPECTRE_V2_USER_CMD_NONE:
@@ -1416,7 +1411,7 @@ spectre_v2_user_select_mitigation(void)
 	 * so allow for STIBP to be selected in those cases.
 	 */
 	if (!boot_cpu_has(X86_FEATURE_STIBP) ||
-	    !smt_possible ||
+	    !cpu_smt_possible() ||
 	    (spectre_v2_in_eibrs_mode(spectre_v2_enabled) &&
 	     !boot_cpu_has(X86_FEATURE_AUTOIBRS)))
 		return;