Commit 73d5e2b4 authored Jul 24, 2018 by Josh Poimboeuf Committed by Peter Zijlstra Jul 24, 2018

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: f048c399 ("x86/topology: Provide topology_smt_supported()")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>

parent 1949f9f4

kernel/cpu.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}