111 ;;Quote: Intel x86 provides segment protection levels and page protection levels

111 ;;Quote: efficient intra-address space protection by combining segmentation and paging hardware

111 ;;Quote: protect the kernel from extension modules by loading each module into a less privileged segment within kernel space

111 ;;Quote: on Intel architectures, an interrupt gate allows user processes to call kernel services

112 ;;Quote: extension modules can access the kernel through a specialized system-call interface; but normally, extensions should be self-contained

112 ;;Quote: the kernel and extension modules share a read-write memory region for non-sensitive data; e.g., packet headers

112 ;;Quote: use page protection to provide access to shared libraries from user-level extensions; data/function pointers stay the same; applications control which pages are accessible

113 ;;Quote: use 'ret' to call a less-privileged extension, and 'call' to return from the extension

113 ;;Quote: 10x cost for hardware-based extensions vs. 40x cost for kernel-process call-return; also, avoids TLB misses

114 ;;Quote: hardware-based extensions need pooled memory allocation