On 2012-06-08 09:47, Michael S. Tsirkin wrote:
> On Mon, Jun 04, 2012 at 01:40:28PM +0200, Jan Kiszka wrote:
>> On 2012-06-04 13:21, Thomas Gleixner wrote:
>>> On Sun, 3 Jun 2012, Avi Kivity wrote:
>>>
>>>> On 06/01/2012 09:26 PM, Jan Kiszka wrote:
>>>>>
>>>>>> you suggesting we need a request_edge_threaded_only_irq() API? Thanks,
>>>>>
>>>>> I'm just wondering if that restriction for threaded IRQs is really
>>>>> necessary for all use cases we have. Threaded MSIs do not appear to me
>>>>> like have to be handled that conservatively, but maybe I'm missing some
>>>>> detail.
>>>>>
>>>>
>>>> btw, I'm hoping we can unthread assigned MSIs. If the delivery is
>>>> unicast, we can precalculate everything and all the handler has to do is
>>>> set the IRR, KVM_REQ_EVENT, and kick the vcpu. All of these can be done
>>>> from interrupt context with just RCU locking.
>>>
>>> There is really no need to run MSI/MSI-X interrupts threaded for
>>> KVM. I'm running the patch below for quite some time and it works like
>>> a charm.
>>>
>>> Thanks,
>>>
>>> tglx
>>> ----
>>> Index: linux-2.6/virt/kvm/assigned-dev.c
>>> ===================================================================
>>> --- linux-2.6.orig/virt/kvm/assigned-dev.c
>>> +++ linux-2.6/virt/kvm/assigned-dev.c
>>> @@ -105,7 +105,7 @@ static irqreturn_t kvm_assigned_dev_thre
>>> }
>>>
>>> #ifdef __KVM_HAVE_MSI
>>> -static irqreturn_t kvm_assigned_dev_thread_msi(int irq, void *dev_id)
>>> +static irqreturn_t kvm_assigned_dev_msi_handler(int irq, void *dev_id)
>>> {
>>> struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
>>>
>>> @@ -117,7 +117,7 @@ static irqreturn_t kvm_assigned_dev_thre
>>> #endif
>>>
>>> #ifdef __KVM_HAVE_MSIX
>>> -static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
>>> +static irqreturn_t kvm_assigned_dev_msix_handler(int irq, void *dev_id)
>>> {
>>> struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
>>> int index = find_index_from_host_irq(assigned_dev, irq);
>>> @@ -346,9 +346,8 @@ static int assigned_device_enable_host_m
>>> }
>>>
>>> dev->host_irq = dev->dev->irq;
>>> - if (request_threaded_irq(dev->host_irq, NULL,
>>> - kvm_assigned_dev_thread_msi, 0,
>>> - dev->irq_name, dev)) {
>>> + if (request_irq(dev->host_irq, kvm_assigned_dev_msi_handler, 0,
>>> + dev->irq_name, dev)) {
>>> pci_disable_msi(dev->dev);
>>> return -EIO;
>>> }
>>> @@ -373,9 +372,9 @@ static int assigned_device_enable_host_m
>>> return r;
>>>
>>> for (i = 0; i < dev->entries_nr; i++) {
>>> - r = request_threaded_irq(dev->host_msix_entries[i].vector,
>>> - NULL, kvm_assigned_dev_thread_msix,
>>> - 0, dev->irq_name, dev);
>>> + r = request_irq(dev->host_msix_entries[i].vector,
>>> + kvm_assigned_dev_msix_handler, 0,
>>> + dev->irq_name, dev);
>>> if (r)
>>> goto err;
>>> }
>>
>> This may work in practice but has two conceptual problems:
>> - we do not want to run a potential broadcast to all VCPUs to run in
>> a host IRQ handler
>> - crazy user space could have configured the route to end up in the
>> PIC or IOAPIC, and both are not hard-IRQ safe (this should probably
>> be caught on setup)
>>
>> So this shortcut requires some checks before being applied to a specific
>> MSI/MSI-X vector.
>
> I did this in the past:
> https://lkml.org/lkml/2012/1/18/287
>
> Have no hw to test this atm but if there are any takers
> wanting to play with it I can update and post.
Just add check that allow only unicasts, and this should be fine.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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