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Illustration of how VMI inlines are used to greatly limit the impact of code change in low level assembler code. Spinlocks, system calls, and the fault handling paths are affected by adding some padding bytes to convert the native instructions into a hook point for the hypervisor to insert shim code. These changes are sufficient to glue the Linux low level entry points to hypervisor event

Illustration of how VMI inlines are used to greatly limit the impact of code change in low level assembler code. Spinlocks, system calls, and the fault handling paths are affected by adding some padding bytes to convert the native instructions into a hook point for the hypervisor to insert shim code. These changes are sufficient to glue the Linux low level entry points to hypervisor event

Unlike full virtualization in which the virtual machine provides the same platform interface as running natively on the hardware, paravirtualization requires modification to the guest operating system to work with the platform interface provided by the hypervisor. Xen was designed with performance in mind. Calls to the hypervisor are minimized, batched if necessary, and non-critical codepaths