RE: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d

["Kay, Allen M" <allen.m.kay@xxxxxxxxx>]

>
>How does this new scheme work? Can it supplant the 
>ioapic_ack=new method?
>Clearly requiring the use of a hacky command-line option to 
>make use of a
>new core feature is not very nice to say the least.
>

Basically, the calls to mask_IO_APIC_irq()/unMask_IO_APIC_irq()
in arch/x86/io_apic.c were replaced with
write_fake_IO_APIC_vector()/restore_real_IO_APIC_vector
- where the fake vector is an unused vector.

Since the global interrupt from chipset only occurs during
masked interrupts, this avoids that chipset bug that cause
you to switch to ioapic_ack=new last year.  I believe it can
supplant ioapic_ack=new method.

>
>I would expect it to work (by design at least) even with 
>ioapic_ack=new.
>

We based our enabling effort on ioapic_ack=old so far.
In theory, it should work with ioapic_ack=new.  I have tried
Ioapic_ack=new but it is not working right now.  We will
be looking into this.

Allen

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