Commit 73d5e2b4 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Peter Zijlstra
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cpu/hotplug: detect SMT disabled by BIOS

If SMT is disabled in BIOS, the CPU code doesn't properly detect it.
The /sys/devices/system/cpu/smt/control file shows 'on', and the 'l1tf'
vulnerabilities file shows SMT as vulnerable.

Fix it by forcing 'cpu_smt_control' to CPU_SMT_NOT_SUPPORTED in such a
case.  Unfortunately the detection can only be done after bringing all
the CPUs online, so we have to overwrite any previous writes to the

Reported-by: default avatarJoe Mario <>
Tested-by: default avatarJiri Kosina <>
Fixes: f048c399

 ("x86/topology: Provide topology_smt_supported()")
Signed-off-by: default avatarJosh Poimboeuf <>
Signed-off-by: default avatarPeter Zijlstra <>
parent 1949f9f4
......@@ -2125,6 +2125,15 @@ 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,
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