Page faults VM exits: PTE A and D bits

Page faults VM exits: PTE A and D bits

Are A and D bits in the corresponding PTE and A bit in the PDE updated when page fault VM exit occurs? Or VM should do this manually when emulating opcode?

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The A and D bits in a PTE are not updated for an instruction that causes a page fault (regardless of whether the page fault causes a VM exit).

The A bit in a PDE may or may not be updated for an instruction that causes a page fault. It is implementation-specific. (Of course, the A bit in PDE may have been set earlier by an access using a different PTE that did not cause a fault.)

Thus, if a VMM handles a page fault by emulating the faulting instruction, it may need to update these bits manually.

David Ott

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