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KVM: fix kvm_vcpu_kick vs __vcpu_run race 

There is a window open between testing of pending IRQ's
and assignment of guest_mode in __vcpu_run.

Injection of IRQ's can race with __vcpu_run as follows:

CPU0                                CPU1
kvm_x86_ops->run()
vcpu->guest_mode = 0                SET_IRQ_LINE ioctl
..
kvm_x86_ops->inject_pending_irq
kvm_cpu_has_interrupt()

                                    apic_test_and_set_irr()
                                    kvm_vcpu_kick
                                    if (vcpu->guest_mode)
                                        send_ipi()

vcpu->guest_mode = 1

So move guest_mode=1 assignment before ->inject_pending_irq, and make
sure that it won't reorder after it.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Marcelo Tosatti 2008-04-11 15:01:22 -03:00 committed by Avi Kivity
parent 62d9f0dbc9
commit e9571ed54b
1 changed files with 14 additions and 2 deletions
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16
arch/x86/kvm/x86.c
View File

@ -2802,6 +2802,13 @@ again:
goto out;
}
vcpu->guest_mode = 1;
/*
* Make sure that guest_mode assignment won't happen after
* testing the pending IRQ vector bitmap.
*/
smp_wmb();
if (vcpu->arch.exception.pending)
__queue_exception(vcpu);
else if (irqchip_in_kernel(vcpu->kvm))
@ -2813,7 +2820,6 @@ again:
up_read(&vcpu->kvm->slots_lock);
vcpu->guest_mode = 1;
kvm_guest_enter();
if (vcpu->requests)
@ -3970,11 +3976,17 @@ static void vcpu_kick_intr(void *info)
void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
{
int ipi_pcpu = vcpu->cpu;
int cpu = get_cpu();
if (waitqueue_active(&vcpu->wq)) {
wake_up_interruptible(&vcpu->wq);
++vcpu->stat.halt_wakeup;
}
if (vcpu->guest_mode)
/*
* We may be called synchronously with irqs disabled in guest mode,
* So need not to call smp_call_function_single() in that case.
*/
if (vcpu->guest_mode && vcpu->cpu != cpu)
smp_call_function_single(ipi_pcpu, vcpu_kick_intr, vcpu, 0, 0);
put_cpu();
}