Commit 36d4fe14 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

x86/bugs: Remove CONFIG_BHI_MITIGATION_AUTO and spectre_bhi=auto 



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: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarNikolay Borisov <nik.borisov@suse.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/412e9dc87971b622bbbaf64740ebc1f140bff343.1712813475.git.jpoimboe@kernel.org
parent 5f882f3b

Documentation/admin-guide/hw-vuln/spectre.rst

+0 −4
Original line number Diff line number Diff line
@@ -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

Documentation/admin-guide/kernel-parameters.txt

+0 −3
Original line number Diff line number Diff line
@@ -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.

arch/x86/Kconfig

+0 −5
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/cpu/bugs.c

+1 −9
Original line number Diff line number Diff line
@@ -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);
@@ -1673,9 +1668,6 @@ 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");