linux-kernel - [PATCH AUTOSEL 5.15 17/42] x86/bugs: Do IBPB fallback check only once

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Date:   Tue, 19 Jul 2022 21:13:25 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>, Borislav Petkov <bp@...e.de>,
        Sasha Levin <sashal@...nel.org>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, peterz@...radead.org,
        pawan.kumar.gupta@...ux.intel.com, kim.phillips@....com,
        alexandre.chartre@...cle.com, sblbir@...zon.com
Subject: [PATCH AUTOSEL 5.15 17/42] x86/bugs: Do IBPB fallback check only once

From: Josh Poimboeuf <jpoimboe@...nel.org>

[ Upstream commit 0fe4aeea9c01baabecc8c3afc7889c809d939bc2 ]

When booting with retbleed=auto, if the kernel wasn't built with
CONFIG_CC_HAS_RETURN_THUNK, the mitigation falls back to IBPB.  Make
sure a warning is printed in that case.  The IBPB fallback check is done
twice, but it really only needs to be done once.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kernel/cpu/bugs.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d4a18649ce9f..c59db48472dc 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -871,8 +871,9 @@ static void __init retbleed_select_mitigation(void)
 			retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
 
 		/*
-		 * The Intel mitigation (IBRS) was already selected in
-		 * spectre_v2_select_mitigation().
+		 * The Intel mitigation (IBRS or eIBRS) was already selected in
+		 * spectre_v2_select_mitigation().  'retbleed_mitigation' will
+		 * be set accordingly below.
 		 */
 
 		break;
-- 
2.35.1