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Paging: Difference between revisions
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Enabling paging in long mode requires a few more additional steps. Since it is not possible to enter long mode without paging with PAE active, the order in which one enables the bits are important. Firstly, paging must not be active (i.e. CR0.PG must be cleared.) Then, CR4.PAE (bit 5) and EFER.LME (bit 8 of MSR 0xC0000080) are set. If 57-bit virtual addresses are to be enabled, then CR4.LA57 (bit 12) is set. Finally, CR0.PG is set to enable paging.
<
; Skip these 3 lines if paging is already disabled
mov ebx, cr0
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hlt ; Done. Replace these lines with your own code
jmp reloadCS
</syntaxhighlight>
Once paging has been enabled, you cannot switch from 4-level paging to 5-level paging (and vice-versa) directly. The same is true for switching to legacy 32-bit paging. You must first disable paging by clearing CR0.PG before making changes. Failure to do so will result in a [[Exceptions#General_Protection_Fault|general protection fault]].
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