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

[Jan Kiszka]

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.

> 
>>  Moreover,
>> different architecture or accelerators may want to overload the delivery
>> handler.
>>
>> Therefore, this commit introduces a delivery hook that is called by the
>> MSI/MSI-X layer when devices send normal messages, but also on spurious
>> deliveries that ended up on the APIC MMIO handler. Our default delivery
>> handler for APIC-based PCs then dispatches between real MSIs and other
>> DMA requests that happened to take the MSI patch.
> 
> 'path'
> 
>>  
>> -static void apic_send_msi(target_phys_addr_t addr, uint32_t data)
>> +void apic_deliver_msi(MSIMessage *msg)
> 
> In general, it is better these days to pass small structures by value.

OK, will adjust this.

> 
> 
> 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).

Jan

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