On Mon, Mar 16, 2009 at 03:12:52PM +0200, Avi Kivity wrote:
> Joerg Roedel wrote:
>> For KVM remote TLB flushes we need to check the KVM_REQ_TLB_FLUSH
>> request flag when the irqs are already disabled. Otherwise there is a
>> small window of time for a race condition where we may enter a guest
>> without doing a requested TLB flush.
>>
>> @@ -3108,8 +3108,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> kvm_write_guest_time(vcpu);
>> if (test_and_clear_bit(KVM_REQ_MMU_SYNC, &vcpu->requests))
>> kvm_mmu_sync_roots(vcpu);
>> - if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
>> - kvm_x86_ops->tlb_flush(vcpu);
>> if (test_and_clear_bit(KVM_REQ_REPORT_TPR_ACCESS,
>> &vcpu->requests)) {
>> kvm_run->exit_reason = KVM_EXIT_TPR_ACCESS;
>> @@ -3133,6 +3131,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> local_irq_disable();
>> + if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests))
>> + kvm_x86_ops->tlb_flush(vcpu);
>> +
>> if (vcpu->requests || need_resched() || signal_pending(current)) {
>> local_irq_enable();
>> preempt_enable();
>>
>
> If we lost the race and someone sets a bit after the test, then the test
> immediately above will pick this up retry the bit tests.
BTW, I've wondered if the local_irq_enable in svm_vcpu_run is safe:
clgi();
local_irq_enable();
There is no way that an interrupt can be handled there without an exit,
right?
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