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

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Fri, Nov 04, 2016 at 06:50:10AM -0600, Jan Beulich wrote:
> >>> 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).

As I've stated in the first paragraph, I think an IO APIC is needed 
for Dom0 to work properly.

Then I don't mind adding an option (disabled by default) if someone believes 
it can run a Dom0 without an IO APIC. In any case, this can always be 
modified later, because IO APIC presence is reported in the MADT, and it's 
not set in stone. 

Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel