Hi Paolo and Sean, Thanks much for your prompt replies and clear explanations. On Tue, Oct 13, 2020 at 2:43 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > No, the logic to find the HPA with a given HVA is the same as the > hardware logic to translate HVA -> HPA. That is it uses the host > "regular" page tables, not the nested page tables. > > In order to translate GPA to HPA, instead, KVM does not use the nested > page tables. I am curious why KVM does not directly use GPAs as HVAs and leverage nested page tables to translate HVAs (i.e., GPAs) to HPAs? Is that because 1) the hardware logic of ``GPA -> [extended/nested page tables] -> HPA[*]'' is different[**] from the hardware logic of ``HVA -> [host regular page tables] -> HPA''; 2) if 1) is true, it is natural to reuse Linux's original functionality to translate HVAs to HPAs through regular page tables. [*]: Here, the translation means the last step for MMU to translate a GVA's corresponding GPA to an HPA through the extended/nested page tables. [**]: To my knowledge, the hardware logic of ``GPA -> [extended/nested page tables] -> HPA'' seems to be the same as the hardware logic of ``HVA -> [host regular page tables] -> HPA''. I appreciate it if you could point out the differences I ignored. Thanks! Best, Harry
