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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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Checking Page Access Permission

There is no performance penalty incurred in order to perform the page privilege and access rights checks. The Paging Unit performs these checks in parallel with address translation. The two sections that follow describe the privilege level and access rights checks.

The Privilege Check

Segment Privilege Check Takes Precedence Over Page Check

The processor always evaluates segment-level protection before performing the page-level protection check. As an example, assume that a segment (code or data) has been defined as 64KB in length and starts on a page boundary (i.e., an address divisible by 4KB). Also assume that the DPL of the segment descriptor is set to three. This means that the segment may be accessed by a ...

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