[PATCH 6.6 113/122] x86/bugs: Remove CONFIG_BHI_MITIGATION_AUTO and spectre_bhi=auto

Greg Kroah-Hartman
2024-04-15T14:37:53Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit 36d4fe147c870f6d3f6602befd7ef44393a1c87a upstream.

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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nikolay 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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Documentation/admin-guide/hw-vuln/spectre.rst | 4 ----
Documentation/admin-guide/kernel-parameters.txt | 3 ---
arch/x86/Kconfig | 4 ----
arch/x86/kernel/cpu/bugs.c | 10 +---------
4 files changed, 1 insertion(+), 20 deletions(-)

--- 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

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5929,9 +5929,6 @@
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] Control mitigation of Spectre variant 2
(indirect branch speculation) vulnerability.
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2584,10 +2584,6 @@ config SPECTRE_BHI_OFF
bool "off"
help
Equivalent to setting spectre_bhi=off command line parameter.
-config SPECTRE_BHI_AUTO
- bool "auto"
- help
- Equivalent to setting spectre_bhi=auto command line parameter.

endchoice

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1624,13 +1624,10 @@ static bool __init spec_ctrl_bhi_dis(voi
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)
{
@@ -1641,8 +1638,6 @@ static int __init spectre_bhi_parse_cmdl
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);

@@ -1672,9 +1667,6 @@ static void __init bhi_select_mitigation
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");