linux-kernel - [tip: x86/urgent] x86/srso: Disable the mitigation on unaffected configurations

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Date:   Mon, 14 Aug 2023 09:37:37 -0000
From:   "tip-bot2 for Borislav Petkov (AMD)" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/srso: Disable the mitigation on unaffected
 configurations

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     e9fbc47b818b964ddff5df5b2d5c0f5f32f4a147
Gitweb:        https://git.kernel.org/tip/e9fbc47b818b964ddff5df5b2d5c0f5f32f4a147
Author:        Borislav Petkov (AMD) <bp@...en8.de>
AuthorDate:    Sun, 13 Aug 2023 12:39:34 +02:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 14 Aug 2023 11:28:51 +02:00

x86/srso: Disable the mitigation on unaffected configurations

Skip the srso cmd line parsing which is not needed on Zen1/2 with SMT
disabled and with the proper microcode applied (latter should be the
case anyway) as those are not affected.

Fixes: 5a15d8348881 ("x86/srso: Tie SBPB bit setting to microcode patch detection")
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/r/20230813104517.3346-1-bp@alien8.de
---
 arch/x86/kernel/cpu/bugs.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d02f73c..6c04aef 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2418,8 +2418,10 @@ static void __init srso_select_mitigation(void)
 		 * IBPB microcode has been applied.
 		 */
 		if ((boot_cpu_data.x86 < 0x19) &&
-		    (!cpu_smt_possible() || (cpu_smt_control == CPU_SMT_DISABLED)))
+		    (!cpu_smt_possible() || (cpu_smt_control == CPU_SMT_DISABLED))) {
 			setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
+			return;
+		}
 	}
 
 	if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
@@ -2696,6 +2698,9 @@ static ssize_t retbleed_show_state(char *buf)
 
 static ssize_t srso_show_state(char *buf)
 {
+	if (boot_cpu_has(X86_FEATURE_SRSO_NO))
+		return sysfs_emit(buf, "Not affected\n");
+
 	return sysfs_emit(buf, "%s%s\n",
 			  srso_strings[srso_mitigation],
 			  (cpu_has_ibpb_brtype_microcode() ? "" : ", no microcode"));