4.18-stable review patch. If anyone has any objections, please let me know.
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From: Josh Poimboeuf jpoimboe@redhat.com
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 jmario@redhat.com Tested-by: Jiri Kosina jkosina@suse.cz Fixes: f048c399e0f7 ("x86/topology: Provide topology_smt_supported()") Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Peter Zijlstra peterz@infradead.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/cpu.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2125,6 +2125,15 @@ static const struct attribute_group cpuh
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); }