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Re: [Xen-devel] [PATCH v3.1 09/15] xen/x86: allow the emulated APICs to be enabled for the hardware domain



>>> On 04.11.16 at 13:09, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Nov 04, 2016 at 04:21:02AM -0600, Jan Beulich wrote:
>> >>> On 04.11.16 at 10:47, <roger.pau@xxxxxxxxxx> wrote:
>> > The local APIC and IO APIC are required in order to deliver interrupts 
>> > from 
>> > physical devices (this is only for PVHv2 hardware domains).
>> 
>> I can see the need for an LAPIC, but I don't think IO-APICs are
>> strictly necessary. Therefore I'd like the option of it being optional
>> at least to be considered (perhaps by way of a brief note in the
>> commit message).
> 
> While it should be possible to run without an IO APIC, AFAICT most USB 
> controllers still only support legacy PCI interrupts, and then the SCI ACPI 
> interrupt is also delivered from a ISA IRQ. I could make the IO APIC 
> optional, but it's going to hinder the functionality of a Dom0 IMHO if 
> disabled.
> 
> What about adding a no-ioapic option to the dom0= list of options?

That's a possible route to go, but mostly orthogonal to the question
here (you talk about mechanism to effect this being optional,
whereas here the question is whether it should be optional in the
first place).

Jan


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