From: Ben Hutchings ben@decadent.org.uk
Add the sched_smt_active() function needed for some x86 speculation mitigations. This was introduced upstream by commits 1b568f0aabf2 "sched/core: Optimize SCHED_SMT", ba2591a5993e "sched/smt: Update sched_smt_present at runtime", c5511d03ec09 "sched/smt: Make sched_smt_present track topology", and 321a874a7ef8 "sched/smt: Expose sched_smt_present static key". The upstream implementation uses the static_key_{disable,enable}_cpuslocked() functions, which aren't practical to backport.
Signed-off-by: Ben Hutchings ben@decadent.org.uk Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@kernel.org Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/sched/smt.h | 18 ++++++++++++++++++ kernel/sched/core.c | 24 ++++++++++++++++++++++++ kernel/sched/sched.h | 1 + 3 files changed, 43 insertions(+) create mode 100644 include/linux/sched/smt.h
--- /dev/null +++ b/include/linux/sched/smt.h @@ -0,0 +1,18 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_SCHED_SMT_H +#define _LINUX_SCHED_SMT_H + +#include <linux/atomic.h> + +#ifdef CONFIG_SCHED_SMT +extern atomic_t sched_smt_present; + +static __always_inline bool sched_smt_active(void) +{ + return atomic_read(&sched_smt_present); +} +#else +static inline bool sched_smt_active(void) { return false; } +#endif + +#endif --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5610,6 +5610,10 @@ static void set_cpu_rq_start_time(void) rq->age_stamp = sched_clock_cpu(cpu); }
+#ifdef CONFIG_SCHED_SMT +atomic_t sched_smt_present = ATOMIC_INIT(0); +#endif + static int sched_cpu_active(struct notifier_block *nfb, unsigned long action, void *hcpu) { @@ -5626,11 +5630,23 @@ static int sched_cpu_active(struct notif * set_cpu_online(). But it might not yet have marked itself * as active, which is essential from here on. */ +#ifdef CONFIG_SCHED_SMT + /* + * When going up, increment the number of cores with SMT present. + */ + if (cpumask_weight(cpu_smt_mask(cpu)) == 2) + atomic_inc(&sched_smt_present); +#endif set_cpu_active(cpu, true); stop_machine_unpark(cpu); return NOTIFY_OK;
case CPU_DOWN_FAILED: +#ifdef CONFIG_SCHED_SMT + /* Same as for CPU_ONLINE */ + if (cpumask_weight(cpu_smt_mask(cpu)) == 2) + atomic_inc(&sched_smt_present); +#endif set_cpu_active(cpu, true); return NOTIFY_OK;
@@ -5645,7 +5661,15 @@ static int sched_cpu_inactive(struct not switch (action & ~CPU_TASKS_FROZEN) { case CPU_DOWN_PREPARE: set_cpu_active((long)hcpu, false); +#ifdef CONFIG_SCHED_SMT + /* + * When going down, decrement the number of cores with SMT present. + */ + if (cpumask_weight(cpu_smt_mask((long)hcpu)) == 2) + atomic_dec(&sched_smt_present); +#endif return NOTIFY_OK; + default: return NOTIFY_DONE; } --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2,6 +2,7 @@ #include <linux/sched.h> #include <linux/sched/sysctl.h> #include <linux/sched/rt.h> +#include <linux/sched/smt.h> #include <linux/sched/deadline.h> #include <linux/mutex.h> #include <linux/spinlock.h>