Re: [PATCH] target/i386: Support up to 32768 CPUs without IRQ remapping

[David Woodhouse]

On Thu, 2020-10-08 at 08:56 +0200, Paolo Bonzini wrote:
> On 05/10/20 16:18, David Woodhouse wrote:
> > +        if (kvm_irqchip_is_split()) {
> > +            ret |= 1U << KVM_FEATURE_MSI_EXT_DEST_ID;
> > +        }
> 
> IIUC this is because in-kernel IOAPIC still doesn't work; and when it
> does, KVM will advertise the feature itself so no other QEMU changes
> will be needed.

More the MSI handling than the IOAPIC. I haven't actually worked out
*what* handles cycles to addresses in the 0xFEExxxxx range for the in-
kernel irqchip and turns them into interrupts (after putting them
through interrupt remapping, if/when the kernel learns to do that).

Ideally the IOAPIC would just swizzle the bits in its RTE to create an
MSI message and pass it on to the same code to be (translated and)
delivered.

You'll note my qemu patch didn't touch IOAPIC code at all, because
qemu's IOAPIC really does just that.

> I queued this, though of course it has to wait for the corresponding
> kernel patches to be accepted (or separated into doc and non-KVM
> parts; we'll see).

Thanks.

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