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xen-devel
Re: Device model architecture (Was Re: [Xen-devel] Re: Are	linkerscripts
 
Ian Pratt wrote:
  > > When switching between the vmcs guest and the minios, we 
just need to 
switch new values into the guest_table variable and the shadow_mode 
variable and then all the Xen logic will do the right 
 
 thing. (no cr3 
flush in incurred)
 
 
 I guess the main logic behind your argument is that there is 
no need to fully virtualize the device models, so no need to 
run them within a non-root VMCS.
 
We can't run them in the same non-root VMCS as the guest since we need
some virtual address space. Since the hardware does a cr3 switch to the
monitor_table when doing a vmexit, wwe might as well make better use of
this and treat the device models as just another paravirtualized guest.
  
 
 I thought some more about this. We can't think of device models as a 
bunch of code that run only during a vmexit. It needs to be able to 
handle asynchronous events such as keyboard/mouse input or other sources 
of events and inject interrupts into the VMX domain ASAP.
 Specifically, on a dual CPU system or a HT system, we should be able to 
run device models on one CPU and the VMX domains on another CPU. This is 
possible in the current design.
        -Arun
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