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 <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e34e75c..be17577 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1989,6 +1989,12 @@
for all guests.
Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
+ kvm-intel.nosmt=[KVM,Intel] If the L1TF CPU bug is present (CVE-2018-3620)
+ and the system has SMT (aka Hyper-Threading) enabled then
+ don't allow guests to be created.
+
+ Default is 0 (allow guests to be created).
+
kvm-intel.ept= [KVM,Intel] Disable extended page tables
(virtualized MMU) support on capable Intel chips.
Default is 1 (enabled)