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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 11, 2009 at 05:24:25PM -0500, Anthony Liguori wrote:
> Michael S. Tsirkin wrote:
>> Here's a draft MSI-X support patch. Among missing features:
>> save/load support, and command-line flag to control the
>> feature. This is on top of qemu-kvm: msi-x is disabled
>> without kvm interrupt injection support for now.
>>   
>
> What's your impression of how much work would be to get this going on  
> top of upstream QEMU?
>
> I'm willing to borrow a few cycles to help out here.  I'd really like to  
> see this series go in via QEMU if possible.

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
	kvm_set_irq
How hard is that?

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);

I would be happy to port my msix code to work on top of this API.
Willing to help?


-- 
MST