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RE: [Xen-devel] [VTD][PATCH] Support intra-domain shared interrupt

>From: Keir Fraser
>Sent: 2007年11月5日 17:45
>On 5/11/07 08:52, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:
>> that situation two devices with different pyhsical IRQs 
>getting aliased
>> to the same guest GSI is hard to occur. And we need one 
>guest GSI mapped
>> to only one physical IRQ, or we can't know which device 
>issues the guest
>> GSI. Ideally, if we can make 1:1 mapping between guest GSI 
>and physcial
>> IRQ, the intra-domain shared interrupt can naturally handled 
>by guest.
>Ah, that's true. I suppose you can assign virtual devfn locations for
>devices to purposely avoid aliasing in GSI space. What do you do about
>aliasing into the ISA IRQ space?
> -- Keir

ISA IRQ alias is less likely to be avoided, since guest OS itself may
program the vPIRQ links. Since it's guest itself to choose using IOAPIC 
or PIC, reverse alias (guest GSI -> physical irq) is inevitable. But we may
not need add extra structures. Just do bit search for all assigned mirqs 
and check whether corresponding girqs matching the EOI gsi. Normally
one domain is only assigned few devices and sharing case should be fewer.
Above walk just adds negligible overhead. :-)


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