[Xen-devel] Shadow Page Tables in Xen

[priya sehgal <priyagps@xxxxxxxxxxx>]

Hi,
I was going through the memory management in Xen and little confused
about shadow page tables for HVM guest and how they work.
Few of my questions are :
1. A shadow page table, is a copy of the guest page table, with actual machine 
frame numbers (MFN), as against the physical page number(PFN) in case of 
guests. 
Do the shadow page tables write protect each of the PTE it contains, or only 
the pages containing the "guest page table" are write protected (to check if 
the guest has modified any entry)? 

2. I know that live migration is supported on xen, but not sure if it works for 
HVM guests. In this case also, xen will need to keep a shadow page table, which 
should detect which pages have been modified since the last time the pages were 
migrated. For this, shadow page table should mark all the PTEs as write 
protected. Does xen implement live migration of HVM guests in this way ? 
If yes, then is this shadow table same as the one used in (1), or there are 
multiple copies of the shadow tables for different purposes?

Thanks.
Priya


      

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