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Modern operating systems are monolithic. Today, however, lack of isolation is one of the main factors undermining security of the kernel. Inherent complexity of the kernel code and rapid development pace combined with the use of unsafe, low-level programming language results in a steady stream of errors. Even after decades of efforts to make commodity kernels more secure, i.e., development of numerous static and dynamic approaches aimed to prevent exploitation of most common errors, several hundreds of serious kernel vulnerabilities are reported every year. Unfortunately, in a monolithic kernel a single exploitable vulnerability potentially provides an attacker with access to the entire kernel.Modern kernels need isolation as a practical means of confining the effects of exploits to individual kernel subsystems. Historically, introducing isolation in the kernel is hard. First, commodity hardware interfaces provide no support for efficient, fine-grained isolation. Second, the complexity of a modern kernel prevents a naive decomposition effort. Our work on Lightweight Execution Domains (LXDs) takes a step towards enabling isolation in a full-featured operating system kernel. LXDs allow one to take an existing kernel subsystem and run it inside an isolated domain with minimal or no modifications and with a minimal overhead. We evaluate our approach by developing isolated versions of several performance-critical device drivers in the Linux kernel.