linux-kernel - [tip: x86/urgent] x86/cpu: Disable BHI mitigation by default when SPECULATION

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Date: Wed, 10 Apr 2024 14:31:18 -0000
From: "tip-bot2 for Sean Christopherson" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>, Ingo Molnar <mingo@...nel.org>,
 Daniel Sneddon <daniel.sneddon@...ux.intel.com>, stable@...r.kernel.org,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/cpu: Disable BHI mitigation by default when
 SPECULATION_MITIGATIONS=n

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     e8f2ec1cc10e86adfc2089fb93a1158e69989bbd
Gitweb:        https://git.kernel.org/tip/e8f2ec1cc10e86adfc2089fb93a1158e69989bbd
Author:        Sean Christopherson <seanjc@...gle.com>
AuthorDate:    Tue, 09 Apr 2024 10:51:06 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 10 Apr 2024 16:22:56 +02:00

x86/cpu: Disable BHI mitigation by default when SPECULATION_MITIGATIONS=n

Rework the initialization of bhi_mitigation to use positive CONFIG tests
for the ON/AUTO cases so that lack of *any* CONFIG_SPECTRE_BHI_* #define,
i.e. when the kernel is built with CONFIG_SPECULATION_MITIGATIONS=n,
results in the mitigation being OFF by default, not AUTO.

Per the help text for SPECULATION_MITIGATIONS, the intent is that 'N'
disables all mitigations.

Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Daniel Sneddon <daniel.sneddon@...ux.intel.com>
Cc: stable@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/r/20240409175108.1512861-3-seanjc@google.com
---
 arch/x86/kernel/cpu/bugs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 27f5004..7e4a706 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1630,9 +1630,9 @@ enum bhi_mitigations {
 };
 
 static enum bhi_mitigations bhi_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_SPECTRE_BHI_ON)  ? BHI_MITIGATION_ON  :
-	IS_ENABLED(CONFIG_SPECTRE_BHI_OFF) ? BHI_MITIGATION_OFF :
-					     BHI_MITIGATION_AUTO;
+	IS_ENABLED(CONFIG_SPECTRE_BHI_ON)   ? BHI_MITIGATION_ON  :
+	IS_ENABLED(CONFIG_SPECTRE_BHI_AUTO) ? BHI_MITIGATION_AUTO :
+					      BHI_MITIGATION_OFF;
 
 static int __init spectre_bhi_parse_cmdline(char *str)
 {