KVM: Use the scheduler preemption notifiers to make kvm preemptible

Current kvm disables preemption while the new virtualization registers are
in use.  This of course is not very good for latency sensitive workloads (one
use of virtualization is to offload user interface and other latency
insensitive stuff to a container, so that it is easier to analyze the
remaining workload).  This patch re-enables preemption for kvm; preemption
is now only disabled when switching the registers in and out, and during
the switch to guest mode and back.

Contains fixes from Shaohua Li <shaohua.li@intel.com>.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/kvm/Kconfig b/drivers/kvm/Kconfig
index 0a419a0de603..8749fa4ffcee 100644
--- a/drivers/kvm/Kconfig
+++ b/drivers/kvm/Kconfig
@@ -17,6 +17,7 @@ if VIRTUALIZATION
 config KVM
         tristate "Kernel-based Virtual Machine (KVM) support"
         depends on X86 && EXPERIMENTAL
+        select PREEMPT_NOTIFIERS
         select ANON_INODES
         ---help---
           Support hosting fully virtualized guest machines using hardware