Current IO emulation is synchronous. The user VM need to wait for the
completion of the the I/O request before return. But Virtio Spec
introduces introduces asynchronous IO with a new register in MMIO/PIO
space named NOTIFY, to be used for FE driver to notify BE driver, ACRN
hypervisor can emulate this register by sending a notification to vCPU
in Service VM side. This way, FE side can resume to work without waiting
for the full completion of BE side response.
Tracked-On: #8209
Signed-off-by: Conghui <conghui.chen@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>
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