Protection: Virtual Memory and Virtual Machines Slide Sources: Based on “Computer Architecture” by Hennessy/Patterson. Supplemented from various freely downloadable sources Security and Privacy and System software •Innovations in Computer Architecture Virtual Memory •Protection through Virtual Machines •Protection from requirements –Architectural –Performance Protection via Virtual Memory •Processes program –Running (state) needed to continue running it –Environment from each other •Protect Processes based virtual memory including TLB which caches page table entries –Page –Example: Segmentation and paging in 80x86 Processes share hardware without interfering with each other and Kernel Process •Provide User Process •Readable portion of Processor state: supervisor mode bit –User enable/disable bit –Exception protection information –Memory to transfer to supervisor mode •System call like normal subroutine to user mode –Return to limit memory access •Mechanism Memory protection Memory •Virtual on each page entry in page table –Restriction write, execute privileges –Read, OS can update page table –Only
Protection: Virtual Memory and Virtual Machines Slide Sources: Based on “Computer Architecture” by Hennessy/Patterson. Supplemented from various freely downloadable sources Security and Privacy •Innovations in Computer Architecture and System software •Protection through Virtual Memory •Protection from Virtual Machines –Architectural requirements –Performance Protection via Virtual Memory •Processes –Running program –Environment (state) needed to continue running it •Protect Processes from each other –Page based virtual memory including TLB which caches page table entries –Example: Segmentation and paging in 80x86 Processes share hardware without interfering with each other •Provide User Process and Kernel Process •Readable portion of Processor state: –User supervisor mode bit –Exception enable/disable bit –Memory protection information •System call to transfer to supervisor mode –Return like normal subroutine to user mode •Mechanism to limit memory access Memory protection •Virtual Memory –Restriction on each page entry in page table –Read, write, execute privileges –Only OS can update page table
protection-virtual-memory-and-virtual-machines.docx