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@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 17 ++++++++++-------
include/linux/kvm_host.h | 1 +
2 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6b2ce1d..307094a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4499,13 +4499,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (vcpu->fpu_active)
kvm_load_guest_fpu(vcpu);
- local_irq_disable();
+ atomic_set(&vcpu->guest_mode, 1);
+ smp_wmb();
- clear_bit(KVM_REQ_KICK, &vcpu->requests);
- smp_mb__after_clear_bit();
+ local_irq_disable();
- 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;
@@ -4550,7 +4552,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
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;
@@ -5470,7 +5473,7 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
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();
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ce027d5..a020fa2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -81,6 +81,7 @@ struct kvm_vcpu {
int vcpu_id;
struct mutex mutex;
int cpu;
+ atomic_t guest_mode;
struct kvm_run *run;
unsigned long requests;
unsigned long guest_debug;
--
1.7.0.4
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