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Re: [Qemu-ppc] [PATCH 0/2] RFC: powerpc-vfio: adding support

From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] [PATCH 0/2] RFC: powerpc-vfio: adding support
Date: Thu, 12 Jul 2012 14:58:47 +1000
User-agent: Mozilla/5.0 (X11; Linux i686; rv:13.0) Gecko/20120614 Thunderbird/13.0.1

On 12/07/12 14:43, Alex Williamson wrote:
> On Thu, 2012-07-12 at 14:38 +1000, Alexey Kardashevskiy wrote:
>> On 12/07/12 14:31, Alex Williamson wrote:
>>> On Thu, 2012-07-12 at 14:16 +1000, Alexey Kardashevskiy wrote:
>>>> On 12/07/12 12:54, Alex Williamson wrote:
>>>>> On Wed, 2012-07-11 at 12:25 +1000, Alexey Kardashevskiy wrote:
>>>>>> On 11/07/12 02:57, Alex Williamson wrote:
>>>>>>> On Tue, 2012-07-10 at 15:51 +1000, Alexey Kardashevskiy wrote:
>>>>>>>> The two patches in this set are supposed to add VFIO support for POWER.
>>>>>>>> The first one adds one more step in the initalizaion sequence which I 
>>>>>>>> am not
>>>>>>>> sure is correct.
>>>>>>>> The second patch adds actual VFIO support. It is not ready to submit 
>>>>>>>> but
>>>>>>>> ready to discuss. I would like to get rid of all #ifdef TARGET_PPC64 
>>>>>>>> in patch #2
>>>>>>>> and I wonder if there is any plan to implement some generic EOI 
>>>>>>>> support code, etc.
>>>>>>> A generic EOI notifier is on my todo list, but I have no idea what it's
>>>>>>> going to look like.  As you know, I've got an ioapic specific notifier
>>>>>>> in my tree, you add a spapr specific one.  I welcome ideas on how to
>>>>>>> create something generic that has a chance of being accepted.  Thanks,
>>>>>> So far the only platform specific call is xxxx_add_gsi_eoi_notifier. The
>>>>>> xxxx_remove_gsi_eoi_notifier only calls notifier_remove, you've got to 
>>>>>> fix yours
>>>>>> ioapic_remove_gsi_eoi_notifier() as it does too much :)
>>>>>> The only place for placing "add_eoi" callback I can see right now is 
>>>>>> QEMUMachine as there is no
>>>>>> unified machine interrupt controller - IOAPIC has its own type 
>>>>>> TYPE_IOAPIC_COMMON and XICS is not
>>>>>> even a SysBusDevice. And the callback is not specific for any kind of 
>>>>>> bus so it cannot go to PCIBus.
>>>>>> Does it sound reasonable?
>>>>> I suspect we'd need to somehow tie it into qemu_irq where both handlers
>>>>> and notifiers are allocated so we don't really care the underlying
>>>>> implementation.  Something like qemu_add_irq_eoi_notifier(qemu_irq
>>>>> irq, ...).  It's another mess like adding the PCIBus interrupt line to
>>>>> gsi effort though.  Thanks,
>>>> Tried. Added add_eoi_notifier() callback to qemu_irq, new IRQ allocator:
>>>> qemu_irq *qemu_allocate_irqs2(qemu_irq_handler handler, void *opaque, int 
>>>> n,
>>>>                               qemu_eoi_add_notifier add_notifier);
>>>> and called it from the XICS initialization code.
>>>> It could work out if pci_get_irq() or pci_route_irq_fn() returned qemu_irq 
>>>> but no, they just return
>>>> a global IRQ number (pure or embedded in a struct) and there is no common 
>>>> way to resolve qemu_irq
>>>> (and then add_eoi_notifier()) from that number within vfio_pci.
>>> Well GSI and qemu_irq are different address spaces.  We still need GSI
>>> for any kind of qemu bypass case.
>> No, that is ok, we also need GSI because XICS and IOAPIC need it in the end.
>>>> May be we could add the callback pointer into PCIINTxRoute?
>>> Maybe, but why is this PCI specific?  Can't we call it as
>>> qemu_add_irq_eoi_notifier(pdev->irq[0], Notifier)?  That would work much
>>> like qemu_set_irq, extracting the irq number from the IRQState and
>>> passing it through to the add_notifier callback for IRQState until it
>>> got to the ioapic/pic/xics.
>>> int qemu_add_irq_eoi_notifier(qemu_irq *irq, Notifier notifier)
>>> {
>>>     if (!irq || !irq->add_eoi_notifier)
>>>         return -1;
>>>    return irq->add_eoi_notifier(irq->opaque, irq->n, notifier);
>>> }
>> Then we will have to entirely replace qemu_allocate_irqs() with 
>> qemu_allocate_irqs2() and pass some
>> non-zero add_eoi_notifier() on every level, at least for PCI for now. I 
>> would like to avoid that if
>> possible - hard to get accepted :)
> Yep, that's why I said it was the same kind of mess as the PCIBus intx
> routing.  It's intrusive, but qemu_irq is the common interrupt model so
> we need to make use of it.

There are 2 level of intrusion.

1. Fix PCIINTxRoute to return the GSI's qemu_irq as well.

2. Add add_eoi_notifier to all levels including PCI. As a part of this, we will 
have to add this
callback to all pci_register_bus() calls to reach global interrupts via 
platform-specific PCI bus.

I would stay with 1). Is that bad?

> A callback on QEMUMachine seems completely
> random.  Thanks,

True :)


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