KVM: Get rid of KVM_REQ_KICK
KVM_REQ_KICK poisons vcpu->requests by having a bit set during normal
operation. This causes the fast path check for a clear vcpu->requests
to fail all the time, triggering tons of atomic operations.
Fix by replacing KVM_REQ_KICK with a vcpu->guest_mode atomic.
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 63c87ad..fc5611b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4604,13 +4604,15 @@
if (vcpu->fpu_active)
kvm_load_guest_fpu(vcpu);
+ atomic_set(&vcpu->guest_mode, 1);
+ smp_wmb();
+
local_irq_disable();
- clear_bit(KVM_REQ_KICK, &vcpu->requests);
- smp_mb__after_clear_bit();
-
- if (vcpu->requests || need_resched() || signal_pending(current)) {
- set_bit(KVM_REQ_KICK, &vcpu->requests);
+ if (!atomic_read(&vcpu->guest_mode) || vcpu->requests
+ || need_resched() || signal_pending(current)) {
+ atomic_set(&vcpu->guest_mode, 0);
+ smp_wmb();
local_irq_enable();
preempt_enable();
r = 1;
@@ -4655,7 +4657,8 @@
if (hw_breakpoint_active())
hw_breakpoint_restore();
- set_bit(KVM_REQ_KICK, &vcpu->requests);
+ atomic_set(&vcpu->guest_mode, 0);
+ smp_wmb();
local_irq_enable();
++vcpu->stat.exits;
@@ -5580,7 +5583,7 @@
me = get_cpu();
if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
- if (!test_and_set_bit(KVM_REQ_KICK, &vcpu->requests))
+ if (atomic_xchg(&vcpu->guest_mode, 0))
smp_send_reschedule(cpu);
put_cpu();
}