Re: [Qemu-devel] [RFC][PATCH 11/45] msi: Factor out delivery hook

[Jan Kiszka]

On 2011-10-17 13:22, Avi Kivity wrote:
> On 10/17/2011 01:15 PM, Jan Kiszka wrote:
>> On 2011-10-17 12:56, Avi Kivity wrote:
>>> On 10/17/2011 11:27 AM, Jan Kiszka wrote:
>>>> So far we deliver MSI messages by writing them into the target MMIO
>>>> area. This reflects what happens on hardware, but imposes some
>>>> limitations on the emulation when introducing KVM in-kernel irqchip
>>>> models. For those we will need to track the message origin.
>>>
>>> Why do we need to track the message origin?  Emulated interrupt remapping?
>>
>> The origin holds the routing cache which we need to track if the message
>> already has a route (and that without searching long lists) and to
>> update that route instead of add another one.
> 
> Okay, having read more of the code I understand this better.  The
> approach of providing an explicit cache entry, while more intrusive, is
> simpler (at least, without std::unordered_map).  However you do need
> destructors for the cache to let the core know that it can't reference
> it anymore.

See my other mail.

> 
> 
>>
>>>
>>>
>>> Not sure what the gain is from intercepting the msi just before the
>>> stl_phys() vs. in the apic handler.
>>
>> APIC is x86-specific, MSI is not. I think Xen will also want to make use
>> of this hook. I originally though of using it for the KVM in-kernel
>> models as well, but I will now establish a callback at APIC-level
>> (upstream will look differently from qemu-kvm in this regard).
>>
> 
> But you still have to handle it the the platform interrupt controller
> (or whatever processes msi messages) since you can still DMA there.  So
> you don't get away from doing it there anyway.

Right, but that's the slow path (which is still handled - on x86 via the
MMIO region the APIC still maintains).

Jan

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