Re: About two-dimensional page translation (e.g., Intel EPT) and shadow page table in Linux QEMU/KVM

[harry harry]

Hi Sean,

Thanks for the explanations. Please see my comments below. Thanks!

>  When TDP (EPT) is used, the
> hardware MMU has two parts: the TDP PTEs that are controlled by KVM, and the 
> IA32
> PTEs that are controlled by the guest.  And there's still a KVM MMU for the 
> guest;
> the KVM MMU in that case knows how to connfigure the TDP PTEs in hardware 
> _and_
> walk the guest IA32 PTEs, e.g. to handle memory accesses during emulation.

Sorry, I could not understand why the emulated MMU is still needed
when TDP (e.g., Intel EPT) is used?
In particular, in what situations, we need the emulated MMU to
configure the TDP PTEs in hardware and walk the guest IA32 PTEs?
Why do we need the emulated MMU in these situations?

Best,
Harry