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Subject[GIT pull] cpu hotplug updates for 5.0
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Date
Linus,

please pull the latest smp-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git smp-urgent-for-linus

Two fixes for the cpu hotplug machinery:

- Replace the overly clever 'SMT disabled by BIOS' detection logic as it
breaks KVM scenarios and prevents speculation control updates when the
Hyperthreads are brought online late after boot.

- Remove a redundant invocation of the speculation control update function.

Thanks,

tglx

------------------>
Josh Poimboeuf (1):
cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVM

Zhenzhong Duan (1):
x86/speculation: Remove redundant arch_smt_update() invocation


arch/x86/kernel/cpu/bugs.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 3 ++-
include/linux/cpu.h | 2 --
kernel/cpu.c | 38 +++++---------------------------------
kernel/sched/fair.c | 1 +
kernel/smp.c | 2 --
6 files changed, 9 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 1de0f4170178..01874d54f4fd 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -71,7 +71,7 @@ void __init check_bugs(void)
* identify_boot_cpu() initialized SMT support information, let the
* core code know.
*/
- cpu_smt_check_topology_early();
+ cpu_smt_check_topology();

if (!IS_ENABLED(CONFIG_SMP)) {
pr_info("CPU: ");
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4341175339f3..95d618045001 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -26,6 +26,7 @@
#include <linux/mod_devicetable.h>
#include <linux/mm.h>
#include <linux/sched.h>
+#include <linux/sched/smt.h>
#include <linux/slab.h>
#include <linux/tboot.h>
#include <linux/trace_events.h>
@@ -6823,7 +6824,7 @@ static int vmx_vm_init(struct kvm *kvm)
* Warn upon starting the first VM in a potentially
* insecure environment.
*/
- if (cpu_smt_control == CPU_SMT_ENABLED)
+ if (sched_smt_active())
pr_warn_once(L1TF_MSG_SMT);
if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER)
pr_warn_once(L1TF_MSG_L1D);
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 218df7f4d3e1..5041357d0297 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -180,12 +180,10 @@ enum cpuhp_smt_control {
#if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT)
extern enum cpuhp_smt_control cpu_smt_control;
extern void cpu_smt_disable(bool force);
-extern void cpu_smt_check_topology_early(void);
extern void cpu_smt_check_topology(void);
#else
# define cpu_smt_control (CPU_SMT_ENABLED)
static inline void cpu_smt_disable(bool force) { }
-static inline void cpu_smt_check_topology_early(void) { }
static inline void cpu_smt_check_topology(void) { }
#endif

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 91d5c38eb7e5..d1c6d152da89 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -376,9 +376,6 @@ 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);
-
-static bool cpu_smt_available __read_mostly;

void __init cpu_smt_disable(bool force)
{
@@ -397,25 +394,11 @@ void __init cpu_smt_disable(bool force)

/*
* The decision whether SMT is supported can only be done after the full
- * CPU identification. Called from architecture code before non boot CPUs
- * are brought up.
- */
-void __init cpu_smt_check_topology_early(void)
-{
- if (!topology_smt_supported())
- cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
-}
-
-/*
- * If SMT was disabled by BIOS, detect it here, after the CPUs have been
- * brought online. This ensures the smt/l1tf sysfs entries are consistent
- * with reality. cpu_smt_available is set to true during the bringup of non
- * boot CPUs when a SMT sibling is detected. Note, this may overwrite
- * cpu_smt_control's previous setting.
+ * CPU identification. Called from architecture code.
*/
void __init cpu_smt_check_topology(void)
{
- if (!cpu_smt_available)
+ if (!topology_smt_supported())
cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
}

@@ -428,18 +411,10 @@ early_param("nosmt", smt_cmdline_disable);

static inline bool cpu_smt_allowed(unsigned int cpu)
{
- if (topology_is_primary_thread(cpu))
+ if (cpu_smt_control == CPU_SMT_ENABLED)
return true;

- /*
- * If the CPU is not a 'primary' thread and the booted_once bit is
- * set then the processor has SMT support. Store this information
- * for the late check of SMT support in cpu_smt_check_topology().
- */
- if (per_cpu(cpuhp_state, cpu).booted_once)
- cpu_smt_available = true;
-
- if (cpu_smt_control == CPU_SMT_ENABLED)
+ if (topology_is_primary_thread(cpu))
return true;

/*
@@ -2090,10 +2065,8 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
*/
cpuhp_offline_cpu_device(cpu);
}
- if (!ret) {
+ if (!ret)
cpu_smt_control = ctrlval;
- arch_smt_update();
- }
cpu_maps_update_done();
return ret;
}
@@ -2104,7 +2077,6 @@ static int cpuhp_smt_enable(void)

cpu_maps_update_begin();
cpu_smt_control = CPU_SMT_ENABLED;
- arch_smt_update();
for_each_present_cpu(cpu) {
/* Skip online CPUs and CPUs on offline nodes */
if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 50aa2aba69bd..310d0637fe4b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5980,6 +5980,7 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p

#ifdef CONFIG_SCHED_SMT
DEFINE_STATIC_KEY_FALSE(sched_smt_present);
+EXPORT_SYMBOL_GPL(sched_smt_present);

static inline void set_idle_cores(int cpu, int val)
{
diff --git a/kernel/smp.c b/kernel/smp.c
index 163c451af42e..f4cf1b0bb3b8 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -584,8 +584,6 @@ void __init smp_init(void)
num_nodes, (num_nodes > 1 ? "s" : ""),
num_cpus, (num_cpus > 1 ? "s" : ""));

- /* Final decision about SMT support */
- cpu_smt_check_topology();
/* Any cleanup work */
smp_cpus_done(setup_max_cpus);
}
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