When the address eld contains a 20 bit physical page

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Unformatted text preview: hin cache block Cache index Cache tag 497 Symbol Æ Å È ¾Ò ¾Ô ¾Ñ Symbol VPO VPN TLBI TLBT Symbol PPO PPN CO CI CT Figure 10.12: Summary of address translation symbols. access any page, but processes running in user mode are only allowed to access pages for which SUP is 0. The READ and WRITE bits control read and write access to the page. For example, if process is running in user mode, then it has permission to read VP 0 and to read or write VP 1. However, it is not allowed to access VP 2. If an instruction violates these permissions, then the CPU triggers a general protection fault that transfers control to an exception handler in the kernel. Unix shells typically report this exception as a “segmentation fault.” 10.6 Address Translation This section covers the basics of address translation. Our aim is to give you an appreciation of the hardware’s role in supporting virtual memory, with enough detail so that you can work through some concrete examples by hand. However, keep in mind that we are omitting a number of details, especially...
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