Enhancing source code quality of operating systems (OSes) is an essential and endless task in communities of commodity OSes. Unfortunately, improving the quality of the kernel code is not trivial because the kernel is large and complex. In particular, asynchronous events from peripheral devices such as interrupts make the improvement quite hard due to their low reproducibility. This paper presents Foxy Feed, a mechanism based on virtual machine monitors that helps to fix bugs caused by asynchronous device-level events. Foxy Feed forges device-level events and injects them to a debuggee kernel at the timing specified in advance, and allows us to control the timing at which asynchronous events occur for the debugging purpose. Using our prototype implementation of Foxy Feed, which is based on Xen 4.1.0, we demonstrate that Foxy Feed reproduces failures caused by device-triggered bugs in Linux and gives significant clues to the root causes.