linux-kernel - [PATCH] x86/srso: Correct the mitigation status when SMT is disabled

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Date:   Tue, 15 Aug 2023 11:57:24 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Nikolay Borisov <nik.borisov@...e.com>, X86 ML <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/srso: Correct the mitigation status when SMT is disabled

On Mon, Aug 14, 2023 at 11:17:27PM +0200, Borislav Petkov wrote:
> Lemme see how ugly it becomes tomorrow.

Not too bad, considering bugs.c's ugliness.

From: "Borislav Petkov (AMD)" <bp@...en8.de>
Date: Tue, 15 Aug 2023 11:53:13 +0200
Subject: [PATCH] x86/srso: Correct the mitigation status when SMT is disabled

Specify how is SRSO mitigated when SMT is disabled. Also, correct the
SMT check for that.

Fixes: e9fbc47b818b ("x86/srso: Disable the mitigation on unaffected configurations")
Suggested-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/kernel/cpu/bugs.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6c04aef4b63b..dc8f874fdd63 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2417,8 +2417,7 @@ static void __init srso_select_mitigation(void)
 		 * Zen1/2 with SMT off aren't vulnerable after the right
 		 * IBPB microcode has been applied.
 		 */
-		if ((boot_cpu_data.x86 < 0x19) &&
-		    (!cpu_smt_possible() || (cpu_smt_control == CPU_SMT_DISABLED))) {
+		if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
 			setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
 			return;
 		}
@@ -2698,8 +2697,12 @@ 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");
+	if (boot_cpu_has(X86_FEATURE_SRSO_NO)) {
+		if (sched_smt_active())
+			return sysfs_emit(buf, "Not affected\n");
+		else
+			return sysfs_emit(buf, "Mitigation: SMT disabled\n");
+	}
 
 	return sysfs_emit(buf, "%s%s\n",
 			  srso_strings[srso_mitigation],
-- 
2.42.0.rc0.25.ga82fb66fed25

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette