linux-kernel - [PATCH 2/3] x86/cpu: Disable BHI mitigation by default when SPECULATION

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Date: Tue,  9 Apr 2024 10:51:06 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jonathan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Sean Christopherson <seanjc@...gle.com>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>
Subject: [PATCH 2/3] 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")
Cc: stable@...r.kernel.org
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Daniel Sneddon <daniel.sneddon@...ux.intel.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.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 295463707e68..e1775debeafe 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)
 {
-- 
2.44.0.478.gd926399ef9-goog