[Xen-devel] Question About Shadow Page Table OOS Optimization

["zhujun" <zhujun@xxxxxxxxxxxxxx>]

Hi, Friends

         I am going over shadow page table code and have a question about oos optimization. When shadow page table is established, if a guest page table entry marked as Dirty=0, the corresponding shadow page table entry clears R/W bit. Thus, when the guest modifies the page frame, xen’s page fault handler marks the guest page table’s entry as Dirty=1. Also, the guest page table is put into oos list. My question is if the guest clears the Dirty bit, how does hypervisor know it and when is the Dirty bit set again? If guest os modifies the page frame again, does the guest page table entry’s Dirty bit reflect this information immediately?

 

zhujun

 

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