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authorJosh Poimboeuf <jpoimboe@redhat.com>2018-07-24 18:17:40 +0200
committerPeter Zijlstra <peterz@infradead.org>2018-07-24 18:17:40 +0200
commit73d5e2b472640b1fcdb61ae8be389912ef211bda (patch)
treea0b859dfb525e4a89dc068194177108d5745f46d /kernel/cpu.c
parent1949f9f49792d65dba2090edddbe36a5f02e3ba3 (diff)
downloadlinux-73d5e2b472640b1fcdb61ae8be389912ef211bda.tar.bz2
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 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>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 37eec872042b..2bc3d2f5b2a5 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -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,
&cpuhp_smt_attr_group);
}