There are no much changes made compared with the original patches. But there do have some issues that we need your kind comments.

1> ACK-NEW method is necessary to avoid IRQ storm. But it causes the deadlock. During my tests, I do find there can be deadlock with patches applied. When assigned a NIC device to HVM domain, the scenario is: Dom0 is waiting to IDE interrupt (vector 0x21); HVM domain is waiting for qemu's IDE emulation and thus blocked; NIC interrupt (MSI vector 0x31) is waiting for injection to HVM domain since it is blocked now; IDE interrupt is waiting for NIC interrupt since NIC interrupt is of high priority but not ACKed by XEN now. When IDE interrupt and NIC interrupt are delivered to the same CPU, and when guest OS is Vista, the phenomenon is easy to be observed.

2> Without ACK-NEW, some naughty NIC devices as we observed will bring IRQ storms. For this phenomenon, I think Yunhong can comment more. Basically, writing EOI without mask the source of MSI will bring IRQ storm. Although the reason is under investigation, XEN should anyhow handle such bogous device, right?

3> Using ACK-OLD and masking the MSI when writing EOI can be solution. However, XEN does not own PCI configuration spaces.