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authorThomas Gleixner <tglx@linutronix.de>2018-08-07 08:19:57 +0200
committerThomas Gleixner <tglx@linutronix.de>2018-08-07 12:25:30 +0200
commitbc2d8d262cba5736332cbc866acb11b1c5748aa9 (patch)
tree2c521cb57923fb4ce065ea4279332ad406f55064 /kernel/cpu.c
parent5b76a3cff011df2dcb6186c965a2e4d809a05ad4 (diff)
downloadlinux-bc2d8d262cba5736332cbc866acb11b1c5748aa9.tar.bz2
cpu/hotplug: Fix SMT supported evaluation
Josh reported that the late SMT evaluation in cpu_smt_state_init() sets cpu_smt_control to CPU_SMT_NOT_SUPPORTED in case that 'nosmt' was supplied on the kernel command line as it cannot differentiate between SMT disabled by BIOS and SMT soft disable via 'nosmt'. That wreckages the state and makes the sysfs interface unusable. Rework this so that during bringup of the non boot CPUs the availability of SMT is determined in cpu_smt_allowed(). If a newly booted CPU is not a 'primary' thread then set the local cpu_smt_available marker and evaluate this explicitely right after the initial SMP bringup has finished. SMT evaulation on x86 is a trainwreck as the firmware has all the information _before_ booting the kernel, but there is no interface to query it. Fixes: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") Reported-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c41
1 files changed, 28 insertions, 13 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 2bc3d2f5b2a5..9d2512dd263c 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -347,6 +347,8 @@ EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
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)
{
if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
@@ -363,14 +365,28 @@ 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.
+ * CPU identification. Called from architecture code before non boot CPUs
+ * are brought up.
*/
-void __init cpu_smt_check_topology(void)
+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.
+ */
+void __init cpu_smt_check_topology(void)
+{
+ if (!cpu_smt_available)
+ cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
+}
+
static int __init smt_cmdline_disable(char *str)
{
cpu_smt_disable(str && !strcmp(str, "force"));
@@ -380,10 +396,18 @@ early_param("nosmt", smt_cmdline_disable);
static inline bool cpu_smt_allowed(unsigned int cpu)
{
- if (cpu_smt_control == CPU_SMT_ENABLED)
+ if (topology_is_primary_thread(cpu))
return true;
- if (topology_is_primary_thread(cpu))
+ /*
+ * 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)
return true;
/*
@@ -2125,15 +2149,6 @@ static const struct attribute_group cpuhp_smt_attr_group = {
static int __init cpu_smt_state_init(void)
{
- /*
- * 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. Note this may overwrite cpu_smt_control's
- * previous setting.
- */
- if (topology_max_smt_threads() == 1)
- cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
-
return sysfs_create_group(&cpu_subsys.dev_root->kobj,
&cpuhp_smt_attr_group);
}