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RE: [Xen-devel] Re: APIC rework

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: RE: [Xen-devel] Re: APIC rework
From: "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
Date: Fri, 20 Nov 2009 09:47:39 +0800
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Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Re: APIC rework
Konrad Rzeszutek Wilk wrote:
> On Wed, Nov 18, 2009 at 11:37:51AM +0800, Zhang, Xiantao wrote:
>> Jeremy Fitzhardinge wrote:
>>> On 11/17/09 06:17, Zhang, Xiantao wrote:
>>>> Originally, this patch is target to get rid of ioapic changes in
>>>> dom0. Before this patch, GSI irq should be mapped and setup through
>>>> dom0 programming ioapic entries, but it depends on using ioapic
>>>> logic in dom0. And if we remove ioapic logic from dom0,  we need to
>>>> find new way how to setup GSI irq.  And this patch comes out under
>>>> this situation.  The idea is from that in Xen the interface
>>>> MAP_PIRQ_TYPE_MSI is used to build the pirq and irq mapping for MSI
>>>> IRQ for each domain. Since MSI IRQ can be setup through this
>>>> hypercall, and I think  we also can leverage the interface
>>>> MAP_PIRQ_TYPE _GSI to build the mapping for GSI irq. Further
>>>> analysis showes that this interface is only used for assigning
>>>> devices to HVM domain in qemu, and I think it should be Okay for
>>>> dom0 building the mapping between its pirq and irq. One different
>>>> thing for GSI irq is that more info should be provided in the call,
>>>> since GSI IRQ has different trigger-mode and polarity (originally
>>>> it is provided by ioapic write in dom0). Certainly, I also think we
>>>> need to document the related info, and if you agree to the change,
>>>> I am happy to add it. 
>>> I don't think there's any need to overload the existing interface
>>> though.  If we're adding new functionality then we can add a new
>>> interface for it (but with luck we can reuse most of the existing
>>> code to implement it).
>>> If you're already considering a "treat this differently" flag in the
>>> argument, then that's a strong pointer that a new interface is
>>> warranted.
>> Agree, and I also don't object to add a similar interface.
>> Since this existing interface is only used for hvm domain before,
>> and  just want to re-use it for dom. 
> I am pretty sure it is used for PV domains too. Look in
> 'xen_create_msi_irq', which extracts the domain that has a PCI device
> for pass-through and on behalf of that domain makes the
> Furthermore, it is also used by Dom0 for MSI devices.

We mean the call MAP_PIRQ_TYPE_GSI, not MAP_PIRQ_TYPE_MSI. 

> What do you mean by 're-use it for dom'?
Oh, seems the char "0" is missing, should be dom0. 

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