From d90a7a0ec83fb86622cd7dae23255d3c50a99ec8 Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Fri, 13 Jul 2018 16:23:25 +0200 Subject: x86/bugs, kvm: Introduce boot-time control of L1TF mitigations Introduce the 'l1tf=' kernel command line option to allow for boot-time switching of mitigation that is used on processors affected by L1TF. The possible values are: full Provides all available mitigations for the L1TF vulnerability. Disables SMT and enables all mitigations in the hypervisors. SMT control via /sys/devices/system/cpu/smt/control is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled. full,force Same as 'full', but disables SMT control. Implies the 'nosmt=force' command line option. sysfs control of SMT and the hypervisor flush control is disabled. flush Leaves SMT enabled and enables the conditional hypervisor mitigation. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled. flush,nosmt Disables SMT and enables the conditional hypervisor mitigation. SMT control via /sys/devices/system/cpu/smt/control is still possible after boot. If SMT is reenabled or flushing disabled at runtime hypervisors will issue a warning. flush,nowarn Same as 'flush', but hypervisors will not warn when a VM is started in a potentially insecure configuration. off Disables hypervisor mitigations and doesn't emit any warnings. Default is 'flush'. Let KVM adhere to these semantics, which means: - 'lt1f=full,force' : Performe L1D flushes. No runtime control possible. - 'l1tf=full' - 'l1tf-flush' - 'l1tf=flush,nosmt' : Perform L1D flushes and warn on VM start if SMT has been runtime enabled or L1D flushing has been run-time enabled - 'l1tf=flush,nowarn' : Perform L1D flushes and no warnings are emitted. - 'l1tf=off' : L1D flushes are not performed and no warnings are emitted. KVM can always override the L1D flushing behavior using its 'vmentry_l1d_flush' module parameter except when lt1f=full,force is set. This makes KVM's private 'nosmt' option redundant, and as it is a bit non-systematic anyway (this is something to control globally, not on hypervisor level), remove that option. Add the missing Documentation entry for the l1tf vulnerability sysfs file while at it. Signed-off-by: Jiri Kosina Signed-off-by: Thomas Gleixner Tested-by: Jiri Kosina Reviewed-by: Greg Kroah-Hartman Reviewed-by: Josh Poimboeuf Link: https://lkml.kernel.org/r/20180713142323.202758176@linutronix.de --- Documentation/ABI/testing/sysfs-devices-system-cpu | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation/ABI/testing/sysfs-devices-system-cpu') diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 65d9b844ecfd..73318225a368 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -476,6 +476,7 @@ What: /sys/devices/system/cpu/vulnerabilities /sys/devices/system/cpu/vulnerabilities/spectre_v1 /sys/devices/system/cpu/vulnerabilities/spectre_v2 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass + /sys/devices/system/cpu/vulnerabilities/l1tf Date: January 2018 Contact: Linux kernel mailing list Description: Information about CPU vulnerabilities @@ -488,6 +489,9 @@ Description: Information about CPU vulnerabilities "Vulnerable" CPU is affected and no mitigation in effect "Mitigation: $M" CPU is affected and mitigation $M is in effect + Details about the l1tf file can be found in + Documentation/admin-guide/l1tf.rst + What: /sys/devices/system/cpu/smt /sys/devices/system/cpu/smt/active /sys/devices/system/cpu/smt/control -- cgit v1.2.3