From: Thomas Gleixner tglx@linutronix.de
commit a74cfffb03b73d41e08f84c2e5c87dec0ce3db9f upstream.
arch_smt_update() is only called when the sysfs SMT control knob is changed. This means that when SMT is enabled in the sysfs control knob the system is considered to have SMT active even if all siblings are offline.
To allow finegrained control of the speculation mitigations, the actual SMT state is more interesting than the fact that siblings could be enabled.
Rework the code, so arch_smt_update() is invoked from each individual CPU hotplug function, and simplify the update function while at it.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Ingo Molnar mingo@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Andy Lutomirski luto@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Jiri Kosina jkosina@suse.cz Cc: Tom Lendacky thomas.lendacky@amd.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: David Woodhouse dwmw@amazon.co.uk Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Andi Kleen ak@linux.intel.com Cc: Dave Hansen dave.hansen@intel.com Cc: Casey Schaufler casey.schaufler@intel.com Cc: Asit Mallick asit.k.mallick@intel.com Cc: Arjan van de Ven arjan@linux.intel.com Cc: Jon Masters jcm@redhat.com Cc: Waiman Long longman9394@gmail.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Dave Stewart david.c.stewart@intel.com Cc: Kees Cook keescook@chromium.org Link: https://lkml.kernel.org/r/20181125185004.521974984@linutronix.de [bwh: Backported to 4.4: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/bugs.c | 11 +++++------ include/linux/sched/smt.h | 2 ++ kernel/cpu.c | 10 +++++++++- 3 files changed, 16 insertions(+), 7 deletions(-)
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -13,6 +13,7 @@ #include <linux/module.h> #include <linux/nospec.h> #include <linux/prctl.h> +#include <linux/sched/smt.h>
#include <asm/spec-ctrl.h> #include <asm/cmdline.h> @@ -340,16 +341,14 @@ void arch_smt_update(void) return;
mutex_lock(&spec_ctrl_mutex); - mask = x86_spec_ctrl_base; - if (IS_ENABLED(CONFIG_SMP)) + + mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP; + if (sched_smt_active()) mask |= SPEC_CTRL_STIBP; - else - mask &= ~SPEC_CTRL_STIBP;
if (mask != x86_spec_ctrl_base) { pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n", - IS_ENABLED(CONFIG_SMP) ? - "Enabling" : "Disabling"); + mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling"); x86_spec_ctrl_base = mask; on_each_cpu(update_stibp_msr, NULL, 1); } --- a/include/linux/sched/smt.h +++ b/include/linux/sched/smt.h @@ -15,4 +15,6 @@ static __always_inline bool sched_smt_ac static inline bool sched_smt_active(void) { return false; } #endif
+void arch_smt_update(void); + #endif --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -8,6 +8,7 @@ #include <linux/init.h> #include <linux/notifier.h> #include <linux/sched.h> +#include <linux/sched/smt.h> #include <linux/unistd.h> #include <linux/cpu.h> #include <linux/oom.h> @@ -199,6 +200,12 @@ void cpu_hotplug_enable(void) EXPORT_SYMBOL_GPL(cpu_hotplug_enable); #endif /* CONFIG_HOTPLUG_CPU */
+/* + * Architectures that need SMT-specific errata handling during SMT hotplug + * should override this. + */ +void __weak arch_smt_update(void) { } + /* Need to know about CPUs going up/down? */ int register_cpu_notifier(struct notifier_block *nb) { @@ -434,6 +441,7 @@ out_release: cpu_hotplug_done(); if (!err) cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu); + arch_smt_update(); return err; }
@@ -537,7 +545,7 @@ out_notify: __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL); out: cpu_hotplug_done(); - + arch_smt_update(); return ret; }