Re: [PATCH RFC 0/2] qemu-kvm: MSI-X support

[Avi Kivity <avi@redhat.com>]

Michael S. Tsirkin wrote:
> It seems that if I just call apic_deliver_irq each time
> I want to send MSI, things will work.
>
> However, large part of the msix code is managing IRQs versus kernel,
> and I'm not sure it's a wise investment of effort to rip it all out. So
> IMHO, what's missing is API that abstracts managing irq routes in kvm,
> specifically abstract this stuff in some way:
> 	kvm_get_irq_route_gsi
> 	kvm_add_routing_entry
> 	kvm_del_routing_entry
> 	kvm_commit_irq_routes
>   

All these are just games with qemu_irq objects.  Should be a lot simpler 
in userspace.


> 	kvm_set_irq
>   

qemu_set_irq().

> How hard is that?
>   

Should be pretty easy, once you get the hang of qemu_irq.

> For now, this API could be a stub that just stores the routes somewhere,
> and set_irq would call the local apic emulation, along the lines of:
>
> 	uint8_t dest = (addr_lo & MSI_ADDR_DEST_ID_MASK)
> 		>> MSI_ADDR_DEST_ID_SHIFT;
> 	uint8_t vector = (addr_hi & MSI_DATA_VECTOR_MASK)
> 		>> MSI_DATA_VECTOR_SHIFT;
> 	uint8_t dest_mode = (addr_lo >> MSI_ADDR_DEST_MODE_SHIFT) & 0x1;
> 	uint8_t trigger_mode = (data >> MSI_DATA_TRIGGER_SHIFT) & 0x1;
> 	uint8_t delivery_mode = (data >> MSI_DATA_DELIVERY_MODE_SHIFT) &
> 		0x7;
> 	apic_deliver_irq(dest, dest_mode, delivery_mode, vector, 0,
> 			 trigger_mode);
>   

qemu_set_irq() eventually calls a callback that you specify; just set it 
do look up the entry and call apic_deliver_irq.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.