Commit 300a6f27 authored by Jiri Kosina's avatar Jiri Kosina Committed by Greg Kroah-Hartman

x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

commit 53c613fe upstream

STIBP is a feature provided by certain Intel ucodes / CPUs. This feature
(once enabled) prevents cross-hyperthread control of decisions made by
indirect branch predictors.

Enable this feature if

- the CPU is vulnerable to spectre v2
- the CPU supports SMT and has SMT siblings online
- spectre_v2 mitigation autoselection is enabled (default)

After some previous discussion, this leaves STIBP on all the time, as wrmsr
on crossing kernel boundary is a no-no. This could perhaps later be a bit
more optimized (like disabling it in NOHZ, experiment with disabling it in
idle, etc) if needed.

Note that the synchronization of the mask manipulation via newly added
spec_ctrl_mutex is currently not strictly needed, as the only updater is
already being serialized by cpu_add_remove_lock, but let's make this a
little bit more future-proof.
Signed-off-by: default avatarJiri Kosina <>
Signed-off-by: default avatarThomas Gleixner <>
Cc: Peter Zijlstra <>
Cc: Josh Poimboeuf <>
Cc: Andrea Arcangeli <>
Cc:  "WoodhouseDavid" <>
Cc: Andi Kleen <>
Cc: Tim Chen <>
Cc:  "SchauflerCasey" <>
Link: default avatarGreg Kroah-Hartman <>
parent 82647e46
......@@ -34,12 +34,10 @@ static void __init spectre_v2_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
* Our boot-time value of the SPEC_CTRL MSR. We read it once so that any
* writes to SPEC_CTRL contain whatever reserved bits have been set.
u64 __ro_after_init x86_spec_ctrl_base;
/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
u64 x86_spec_ctrl_base;
static DEFINE_MUTEX(spec_ctrl_mutex);
* The vendor and possibly platform specific bits which can be modified in
......@@ -324,6 +322,46 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
return cmd;
static bool stibp_needed(void)
if (spectre_v2_enabled == SPECTRE_V2_NONE)
return false;
if (!boot_cpu_has(X86_FEATURE_STIBP))
return false;
return true;
static void update_stibp_msr(void *info)
wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
void arch_smt_update(void)
u64 mask;
if (!stibp_needed())
mask = x86_spec_ctrl_base;
if (cpu_smt_control == CPU_SMT_ENABLED)
if (mask != x86_spec_ctrl_base) {
pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
cpu_smt_control == CPU_SMT_ENABLED ?
"Enabling" : "Disabling");
x86_spec_ctrl_base = mask;
on_each_cpu(update_stibp_msr, NULL, 1);
static void __init spectre_v2_select_mitigation(void)
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
......@@ -423,6 +461,9 @@ static void __init spectre_v2_select_mitigation(void)
pr_info("Enabling Restricted Speculation for firmware calls\n");
/* Enable STIBP if appropriate */
#undef pr_fmt
......@@ -813,6 +854,8 @@ static ssize_t l1tf_show_state(char *buf)
static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
char *buf, unsigned int bug)
int ret;
if (!boot_cpu_has_bug(bug))
return sprintf(buf, "Not affected\n");
......@@ -827,10 +870,12 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
case X86_BUG_SPECTRE_V2:
return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
ret = sprintf(buf, "%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "",
boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
(x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",
return ret;
return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);
......@@ -2045,6 +2045,12 @@ static void cpuhp_online_cpu_device(unsigned int cpu)
kobject_uevent(&dev->kobj, KOBJ_ONLINE);
* Architectures that need SMT-specific errata handling during SMT hotplug
* should override this.
void __weak arch_smt_update(void) { };
static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
int cpu, ret = 0;
......@@ -2071,8 +2077,10 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
if (!ret)
if (!ret) {
cpu_smt_control = ctrlval;
return ret;
......@@ -2083,6 +2091,7 @@ static int cpuhp_smt_enable(void)
cpu_smt_control = CPU_SMT_ENABLED;
for_each_present_cpu(cpu) {
/* Skip online CPUs and CPUs on offline nodes */
if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment