Re: [PATCH 3/8] KVM: Handle device assignment to guests

Avi Kivity
2008-07-17T06:02:34Z

Han, Weidong wrote:
> Avi Kivity wrote:
>
>>> +static void kvm_pci_pt_work_fn(struct work_struct *work) +{
>>> + struct kvm_pci_pt_dev_list *match;
>>> + struct kvm_pci_pt_work *int_work;
>>> + int source;
>>> + unsigned long flags;
>>> + int guest_irq;
>>> + int host_irq;
>>> +
>>> + int_work = container_of(work, struct kvm_pci_pt_work, work); +
>>> + source = int_work->source ? KVM_PT_SOURCE_IRQ_ACK :
>>> KVM_PT_SOURCE_IRQ; + + /* This is taken to safely inject irq
>>>
> inside
>
>>> the guest. When + * the interrupt injection (or the ioapic code)
>>> uses a + * finer-grained lock, update this
>>> + */
>>> + mutex_lock(&int_work->kvm->lock);
>>> + read_lock_irqsave(&kvm_pci_pt_lock, flags);
>>> + match =
>>>
> kvm_find_pci_pt_dev(&int_work->kvm->arch.pci_pt_dev_head,
>
>>> NULL, + int_work->irq, source);
>>> + if (!match) {
>>> + printk(KERN_ERR "%s: no matching device assigned to
>>>
> guest "
>
>>> + "found for irq %d, source = %d!\n",
>>> + __func__, int_work->irq, int_work->source);
>>> + read_unlock_irqrestore(&kvm_pci_pt_lock, flags); +
>>>
> goto out;
>
>>> + }
>>> + guest_irq = match->pt_dev.guest.irq;
>>> + host_irq = match->pt_dev.host.irq;
>>> + read_unlock_irqrestore(&kvm_pci_pt_lock, flags);
>>> +
>>> + if (source == KVM_PT_SOURCE_IRQ)
>>> + kvm_set_irq(int_work->kvm, guest_irq, 1);
>>> + else {
>>> + kvm_set_irq(int_work->kvm, int_work->irq, 0);
>>> + enable_irq(host_irq);
>>> + }
>>> +out:
>>> + mutex_unlock(&int_work->kvm->lock);
>>> + kvm_put_kvm(int_work->kvm);
>>> +}
>>>
>>> +
>>> +/* FIXME: Implement the OR logic needed to make shared interrupts
>>> on + * this line behave properly + */
>>>
>>>
>> Isn't this a showstopper? There is no easy way for a user to avoid
>> sharing, especially as we have only three pci irqs at present.
>>
>>
>
> Currently it's not easy to avoid sharing. I think we can support MSI for
> assgined device to solve sharing problem.
>

MSI is definitely the right direction, but we also need to support the
OR logic for guests that do not support MSI.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.