Commit a74cfffb authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

x86/speculation: Rework SMT state change 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarIngo 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>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185004.521974984@linutronix.de
parent 321a874a

arch/x86/kernel/cpu/bugs.c

+5 −6
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#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>
@@ -344,16 +345,14 @@ void arch_smt_update(void) 
		return;



	mutex_lock(&spec_ctrl_mutex);

	mask = x86_spec_ctrl_base;

	if (cpu_smt_control == CPU_SMT_ENABLED)



	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",

				cpu_smt_control == CPU_SMT_ENABLED ?

				"Enabling" : "Disabling");

			mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling");

		x86_spec_ctrl_base = mask;

		on_each_cpu(update_stibp_msr, NULL, 1);

	}

include/linux/sched/smt.h

+2 −0
Original line number Diff line number Diff line
@@ -15,4 +15,6 @@ static __always_inline bool sched_smt_active(void) 
static inline bool sched_smt_active(void) { return false; }

#endif



void arch_smt_update(void);



#endif

kernel/cpu.c

+9 −6
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/sched/signal.h>

#include <linux/sched/hotplug.h>

#include <linux/sched/task.h>

#include <linux/sched/smt.h>

#include <linux/unistd.h>

#include <linux/cpu.h>

#include <linux/oom.h>
@@ -367,6 +368,12 @@ static void lockdep_release_cpus_lock(void) 


#endif	/* CONFIG_HOTPLUG_CPU */



/*

 * Architectures that need SMT-specific errata handling during SMT hotplug

 * should override this.

 */

void __weak arch_smt_update(void) { }



#ifdef CONFIG_HOTPLUG_SMT

enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;

EXPORT_SYMBOL_GPL(cpu_smt_control);
@@ -1011,6 +1018,7 @@ out: 
	 * concurrent CPU hotplug via cpu_add_remove_lock.

	 */

	lockup_detector_cleanup();

	arch_smt_update();

	return ret;

}
@@ -1139,6 +1147,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target) 
	ret = cpuhp_up_callbacks(cpu, st, target);

out:

	cpus_write_unlock();

	arch_smt_update();

	return ret;

}
@@ -2055,12 +2064,6 @@ 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;

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