KVM: Add "exiting guest mode" state

Currently we keep track of only two states: guest mode and host
mode.  This patch adds an "exiting guest mode" state that tells
us that an IPI will happen soon, so unless we need to wait for the
IPI, we can avoid it completely.

Also
1: No need atomically to read/write ->mode in vcpu's thread

2: reorganize struct kvm_vcpu to make ->mode and ->requests
   in the same cache line explicitly

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fd67bcde9980..19209f849cf7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -171,7 +171,12 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
                 if (kvm_make_check_request(req, vcpu))
                         continue;
                 cpu = vcpu->cpu;
-                if (cpus != NULL && cpu != -1 && cpu != me)
+
+                /* Set ->requests bit before we read ->mode */
+                smp_mb();
+
+                if (cpus != NULL && cpu != -1 && cpu != me &&
+                      kvm_vcpu_exiting_guest_mode(vcpu) != OUTSIDE_GUEST_MODE)
                         cpumask_set_cpu(cpu, cpus);
         }
         if (unlikely(cpus == NULL))