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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Josh Poimboeuf <jpoimboe@kernel.org>,
        Borislav Petkov <bp@suse.de>,
        Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
        Ben Hutchings <ben@decadent.org.uk>
Subject: [PATCH 5.10 109/148] x86/bugs: Do IBPB fallback check only once
Date:   Sat, 23 Jul 2022 11:55:21 +0200
Message-Id: <20220723095254.884274073@linuxfoundation.org>
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From: Josh Poimboeuf <jpoimboe@kernel.org>

commit 0fe4aeea9c01baabecc8c3afc7889c809d939bc2 upstream.

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@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/cpu/bugs.c |   15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -847,18 +847,13 @@ static void __init retbleed_select_mitig
 	case RETBLEED_CMD_AUTO:
 	default:
 		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
-		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
-
-			if (IS_ENABLED(CONFIG_RETPOLINE) &&
-			    IS_ENABLED(CONFIG_CC_HAS_RETURN_THUNK))
-				retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
-			else
-				retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
-		}
+		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
+			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;