From a0695af3406ae2a08184bd47a9e948fe6f9858b9 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Wed, 20 Jun 2018 11:29:53 -0400 Subject: x86/KVM: Warn user if KVM is loaded SMT and L1TF CPU bug being present commit 26acfb666a473d960f0fd971fe68f3e3ad16c70b upstream If the L1TF CPU bug is present we allow the KVM module to be loaded as the major of users that use Linux and KVM have trusted guests and do not want a broken setup. Cloud vendors are the ones that are uncomfortable with CVE 2018-3620 and as such they are the ones that should set nosmt to one. Setting 'nosmt' means that the system administrator also needs to disable SMT (Hyper-threading) in the BIOS, or via the 'nosmt' command line parameter, or via the /sys/devices/system/cpu/smt/control. See commit 05736e4ac13c ("cpu/hotplug: Provide knobs to control SMT"). Other mitigations are to use task affinity, cpu sets, interrupt binding, etc - anything to make sure that _only_ the same guests vCPUs are running on sibling threads. Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Thomas Gleixner Signed-off-by: David Woodhouse Signed-off-by: Greg Kroah-Hartman --- kernel/cpu.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel') diff --git a/kernel/cpu.c b/kernel/cpu.c index 49acbd2fa81a..8be14464b43c 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -358,6 +358,7 @@ EXPORT_SYMBOL_GPL(cpu_hotplug_enable); #ifdef CONFIG_HOTPLUG_SMT enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED; +EXPORT_SYMBOL_GPL(cpu_smt_control); static int __init smt_cmdline_disable(char *str) { -- cgit v1.2.3