linux-kernel - [PATCH 05/22] x86/srso: Fix SBPB enablement for mitigations=off

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Message-ID: <141c92f20ab46cf0c028e86b946134cd702d0ea5.1692580085.git.jpoimboe@kernel.org>
Date:   Sun, 20 Aug 2023 18:19:02 -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 05/22] x86/srso: Fix SBPB enablement for mitigations=off

If the user has requested no mitigations with mitigations=off, use the
lighter-weight SBPB instead of IBPB for other mitigations.

Note that even with mitigations=off, IBPB/SBPB may still be used for
Spectre v2 user <-> user protection.  Whether that makes sense is a
question for another day.

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/kernel/cpu/bugs.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 10499bcd4e39..ff5bfe8f0ee9 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2496,8 +2496,7 @@ static void __init srso_select_mitigation(void)
 	pr_info("%s%s\n", srso_strings[srso_mitigation], (has_microcode ? "" : ", no microcode"));
 
 pred_cmd:
-	if ((boot_cpu_has(X86_FEATURE_SRSO_NO) || srso_cmd == SRSO_CMD_OFF) &&
-	     boot_cpu_has(X86_FEATURE_SBPB))
+	if (boot_cpu_has(X86_FEATURE_SBPB) && srso_mitigation == SRSO_MITIGATION_NONE)
 		x86_pred_cmd = PRED_CMD_SBPB;
 }
 
-- 
2.41.0