On 17/09/2015 17:58, Radim Krčmář wrote:
> For interrupts from MSI and IOxAPIC:
> - Flat logical interrupts are delivered as if we had natural
> (CPU0<->bit0, CPU1<->bit1, ...) flat logical xAPIC for first 8 VCPUs.
> - Cluster logical doesn't work much, it's interpreted like flat logical.
> I didn't care about xAPIC cluster because Linux, the sole user of our
> paravirtualized x2APIC, doesn't configure it.
>
> I'll paste kvm_apic_mda() source for better explanation:
>
> static u32 kvm_apic_mda(unsigned int dest_id, struct kvm_lapic *source,
> struct kvm_lapic *target)
> {
> bool ipi = source != NULL;
> bool x2apic_mda = apic_x2apic_mode(ipi ? source : target);
>
> if (!ipi && dest_id == APIC_BROADCAST && x2apic_mda)
> return X2APIC_BROADCAST;
>
> return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
> }
>
> MSI/IOxAPIC interrupt means that source is NULL and if the target is in
> x2APIC mode, the original 'dest_id' is returned as mda => a flat logical
> xAPIC to 0x0f will get interpreted as (cluster) logical x2APIC 0xf in
> kvm_apic_match_logical_addr().
> xAPIC address are only 8 bit long so they always get delivered to x2APIC
> cluster 0, where first 16 bits work like xAPIC flat logical mode.
Ok, I was wondering whether this was the correct interpretation. Thanks!
Paolo
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