linux-kernel - [PATCH 15/23] x86/srso: Remove 'pred

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Message-ID: <ec18b04787fc21874303f29746a49847751eddd6.1692919072.git.jpoimboe@kernel.org>
Date:   Fri, 25 Aug 2023 00:01:46 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, David.Kaplan@....com,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Nikolay Borisov <nik.borisov@...e.com>,
        gregkh@...uxfoundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 15/23] x86/srso: Remove 'pred_cmd' label

SBPB is only enabled in two distinct cases:

1) when SRSO has been disabled with srso=off

2) when SRSO has been fixed (in future HW)

Simplify the control flow by getting rid of the 'pred_cmd' label and
moving the SBPB enablement check to the two corresponding code sites.
This makes it more clear when exactly SBPB gets enabled.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d883d1c38f7f..3c7f634b6148 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2410,13 +2410,21 @@ static void __init srso_select_mitigation(void)
 {
 	bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
 
-	if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off())
-		goto pred_cmd;
+	if (cpu_mitigations_off())
+		return;
+
+	if (!boot_cpu_has_bug(X86_BUG_SRSO)) {
+		if (boot_cpu_has(X86_FEATURE_SBPB))
+			x86_pred_cmd = PRED_CMD_SBPB;
+		return;
+	}
 
 	if (has_microcode) {
 		/*
 		 * Zen1/2 with SMT off aren't vulnerable after the right
 		 * IBPB microcode has been applied.
+		 *
+		 * Zen1/2 don't have SBPB, no need to try to enable it here.
 		 */
 		if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
 			setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
@@ -2439,7 +2447,9 @@ static void __init srso_select_mitigation(void)
 
 	switch (srso_cmd) {
 	case SRSO_CMD_OFF:
-		goto pred_cmd;
+		if (boot_cpu_has(X86_FEATURE_SBPB))
+			x86_pred_cmd = PRED_CMD_SBPB;
+		return;
 
 	case SRSO_CMD_MICROCODE:
 		if (has_microcode) {
@@ -2501,11 +2511,6 @@ static void __init srso_select_mitigation(void)
 
 out:
 	pr_info("%s%s\n", srso_strings[srso_mitigation], has_microcode ? "" : ", no microcode");
-
-pred_cmd:
-	if ((!boot_cpu_has_bug(X86_BUG_SRSO) || srso_cmd == SRSO_CMD_OFF) &&
-	     boot_cpu_has(X86_FEATURE_SBPB))
-		x86_pred_cmd = PRED_CMD_SBPB;
 }
 
 #undef pr_fmt
-- 
2.41.0