From: cross@spitfire.i.gajendra.net   
      
   In article ,   
   Dan Cross  wrote:   
   >In article , BGB   wrote:   
   >>On 5/22/2023 3:10 PM, Dan Cross wrote:   
   >>[snip]   
   >>> L2PT's like the EPT and NPT are wins here; even in the nested   
   >>> VM case, where we have to resort to shadow paging techniques, we   
   >>> can handle L2 page faults in the top-level hypervisor.   
   >>>   
   >>   
   >>But, if one uses SW TLB, then NPT (as a concept) has no reason to need   
   >>to exist...   
   >   
   >Yes, at great expense.   
   >   
   >>> There's a reason soft-TLBs have basically disappeared.  :-)   
   >>   
   >>Probably depends some on how the software-managed TLB is implemented.   
   >   
   >Not really; the design issues and the impact are both   
   >well-known.  Think through how a nested guest (note, not a   
   >nested page table, but a recursive instance of a hypervisor)   
   >would be handled.   
      
   Another thing to consider in a virtualized context with a   
   soft-TLB: suppose the host and guest want to occupy the same   
   region of virtual memory.  How does the host wrest control   
   back from the guest, if the guest has usurped the host's   
   mappings?  On MIPS, you have KSEGs, which is one approach   
   here, but note that under (say) Disco you had to modify the   
   guest kernel as a result.   
      
   	- Dan C.   
      
   --- SoupGate-Win32 v1.05   
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