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, 10 insertions, 6 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5eccdba08bd0..a7f65aa6eef6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5210,14 +5210,18 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
                 kvm_load_guest_fpu(vcpu);
         kvm_load_guest_xcr0(vcpu);
 
-        atomic_set(&vcpu->guest_mode, 1);
-        smp_wmb();
+        vcpu->mode = IN_GUEST_MODE;
+
+        /* We should set ->mode before check ->requests,
+         * see the comment in make_all_cpus_request.
+         */
+        smp_mb();
 
         local_irq_disable();
 
-        if (!atomic_read(&vcpu->guest_mode) || vcpu->requests
+        if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
             || need_resched() || signal_pending(current)) {
-                atomic_set(&vcpu->guest_mode, 0);
+                vcpu->mode = OUTSIDE_GUEST_MODE;
                 smp_wmb();
                 local_irq_enable();
                 preempt_enable();
@@ -5253,7 +5257,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
         kvm_get_msr(vcpu, MSR_IA32_TSC, &vcpu->arch.last_guest_tsc);
 
-        atomic_set(&vcpu->guest_mode, 0);
+        vcpu->mode = OUTSIDE_GUEST_MODE;
         smp_wmb();
         local_irq_enable();
 
@@ -6157,7 +6161,7 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 
         me = get_cpu();
         if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
-                if (atomic_xchg(&vcpu->guest_mode, 0))
+                if (kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE)
                         smp_send_reschedule(cpu);
         put_cpu();
 }