[PATCH 6/7] x86/bugs: Remove CONFIG_BHI_MITIGATION_AUTO and spectre_bhi=auto

From: Josh Poimboeuf <jpoimboe@kernel.org>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@linux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Nikolay Borisov <nik.borisov@suse.com>,
	KP Singh <kpsingh@kernel.org>, Waiman Long <longman@redhat.com>,
	Borislav Petkov <bp@alien8.de>
Subject: [PATCH 6/7] x86/bugs: Remove CONFIG_BHI_MITIGATION_AUTO and spectre_bhi=auto
Date: Wed, 10 Apr 2024 22:40:50 -0700	[thread overview]
Message-ID: <412e9dc87971b622bbbaf64740ebc1f140bff343.1712813475.git.jpoimboe@kernel.org> (raw)
In-Reply-To: <cover.1712813475.git.jpoimboe@kernel.org>

Unlike most other mitigations' "auto" options, spectre_bhi=auto only
mitigates newer systems, which is confusing and not particularly useful.

Remove it.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 Documentation/admin-guide/hw-vuln/spectre.rst   |  4 ----
 Documentation/admin-guide/kernel-parameters.txt |  3 ---
 arch/x86/Kconfig                                |  5 -----
 arch/x86/kernel/cpu/bugs.c                      | 10 +---------
 4 files changed, 1 insertion(+), 21 deletions(-)

diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index 5a39acf82483..25a04cda4c2c 100644
--- a/Documentation/admin-guide/hw-vuln/spectre.rst
+++ b/Documentation/admin-guide/hw-vuln/spectre.rst
@@ -669,10 +669,6 @@ kernel command line.
 			needed.
 		off
 			Disable the mitigation.
-		auto
-			Enable the HW mitigation if needed, but
-			*don't* enable the SW mitigation except for KVM.
-			The system may be vulnerable.
 
 For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt
 
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a3874cc97892..902ecd92a29f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6072,9 +6072,6 @@
 			on   - (default) Enable the HW or SW mitigation
 			       as needed.
 			off  - Disable the mitigation.
-			auto - Enable the HW mitigation if needed, but
-			       *don't* enable the SW mitigation except
-			       for KVM.  The system may be vulnerable.
 
 	spectre_v2=	[X86,EARLY] Control mitigation of Spectre variant 2
 			(indirect branch speculation) vulnerability.
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 10a6251f58f3..b63b6767a63d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2651,11 +2651,6 @@ config SPECTRE_BHI_OFF
 	bool "off"
 	help
 	  Equivalent to setting spectre_bhi=off command line parameter.
-config SPECTRE_BHI_AUTO
-	bool "auto"
-	depends on BROKEN
-	help
-	  Equivalent to setting spectre_bhi=auto command line parameter.
 
 endchoice
 
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index efffd87381b1..74ade6d7caa3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1625,13 +1625,10 @@ static bool __init spec_ctrl_bhi_dis(void)
 enum bhi_mitigations {
 	BHI_MITIGATION_OFF,
 	BHI_MITIGATION_ON,
-	BHI_MITIGATION_AUTO,
 };
 
 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 : BHI_MITIGATION_OFF;
 
 static int __init spectre_bhi_parse_cmdline(char *str)
 {
@@ -1642,8 +1639,6 @@ static int __init spectre_bhi_parse_cmdline(char *str)
 		bhi_mitigation = BHI_MITIGATION_OFF;
 	else if (!strcmp(str, "on"))
 		bhi_mitigation = BHI_MITIGATION_ON;
-	else if (!strcmp(str, "auto"))
-		bhi_mitigation = BHI_MITIGATION_AUTO;
 	else
 		pr_err("Ignoring unknown spectre_bhi option (%s)", str);
 
@@ -1682,9 +1677,6 @@ static void __init bhi_select_mitigation(void)
 	setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT);
 	pr_info("Spectre BHI mitigation: SW BHB clearing on vm exit\n");
 
-	if (bhi_mitigation == BHI_MITIGATION_AUTO)
-		return;
-
 	/* Mitigate syscalls when the mitigation is forced =on */
 	setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP);
 	pr_info("Spectre BHI mitigation: SW BHB clearing on syscall\n");
-- 
2.44.0

