From c6613521abbc2685ef334af32e455589d14f1d8d Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 25 Jul 2018 10:36:45 +0200 Subject: [PATCH] cpu/hotplug: detect SMT disabled by BIOS commit 73d5e2b472640b1fcdb61ae8be389912ef211bda upstream 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 variable. Reported-by: Joe Mario Tested-by: Jiri Kosina Fixes: f048c399e0f7 ("x86/topology: Provide topology_smt_supported()") Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman --- kernel/cpu.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/cpu.c b/kernel/cpu.c index 877437989a28..5787d5e043da 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2137,6 +2137,15 @@ 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, &cpuhp_smt_attr_group); }