2015-09-17 16:24+0200, Paolo Bonzini:
> I think kvm_apic_match_logical_addr for MSI and IOAPIC interrupts is
> buggy in x2apic mode.
>
> It does:
>
> if (apic_x2apic_mode(apic))
> return ((logical_id >> 16) == (mda >> 16))
> && (logical_id & mda & 0xffff) != 0;
>
> But mda is only 8-bits for MSI and IOAPIC interrupts.
>
> Radim, should kvm_apic_mda also handle the !ipi && x2apic_mda && dest_id
> != APIC_BROADCAST case? It never triggers with Linux because it uses
> only the physical mode (that's not super-easy to see;
> ioapic_set_affinity looks for the RTEs in irq_data->chip_data and that
> is allocated with kzalloc).
KVM handles that case, it's just convoluted.
(I wish we scrapped the IR-less x2APIC mode.)
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.
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