x86/bugs: Remove CONFIG_BHI_MITIGATION_AUTO and spectre_bhi=auto

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>

diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index 22492b75ff42a447f6dfb755056896e00e9d4008..b038410eccb685679d8239a31192dfa5f37ed2aa 100644 (file)
--- a/Documentation/admin-guide/hw-vuln/spectre.rst
+++ b/Documentation/admin-guide/hw-vuln/spectre.rst
@@ -719,10 +719,6 @@ For user space mitigation:
                        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 2ff2e5056c9759770852875cbb86033cafa210f3..e61f0d038c6d769fe24be5d1aa19f4b724b43153 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5413,9 +5413,6 @@
                        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.

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 591b0a7abfd2c10d67eb220002a24619288bd393..ec740d5263d8b743db7983f6e5694bbd7a85a7c1 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2523,10 +2523,6 @@ 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
 

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index dafb854603f00ac529dc52fbbc13e60f77e3e643..119ae8db01995110c85f19aed0d1abca7fa7d06c 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1602,13 +1602,10 @@ 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)
 {
@@ -1619,8 +1616,6 @@ 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);
 
@@ -1650,9 +1645,6 @@ 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");