| From foo@baz Tue Aug 14 16:14:56 CEST 2018 |
| From: Josh Poimboeuf <jpoimboe@redhat.com> |
| Date: Wed, 25 Jul 2018 12:00:27 +0200 |
| Subject: cpu/hotplug: detect SMT disabled by BIOS |
| |
| From: Josh Poimboeuf <jpoimboe@redhat.com> |
| |
| 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 <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: David Woodhouse <dwmw@amazon.co.uk> |
| 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 |
| @@ -2063,6 +2063,15 @@ 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); |
| } |
