BTW, I still have one more question as follows. Thanks! On Mon, Oct 12, 2020 at 12:54 PM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > No, the guest physical address spaces is not intrinsically tied to the host > virtual address spaces. The fact that GPAs and HVAs are related in KVM is a > property KVM's architecture. EPT/NPT has absolutely nothing to do with HVAs. > > As Maxim pointed out, KVM links a guest's physical address space, i.e. GPAs, to > the host's virtual address space, i.e. HVAs, via memslots. For all intents and > purposes, this is an extra layer of address translation that is purely software > defined. The memslots allow KVM to retrieve the HPA for a given GPA when > servicing a shadow page fault (a.k.a. EPT violation). > > When EPT is enabled, a shadow page fault due to an unmapped GPA will look like: > > GVA -> [guest page tables] -> GPA -> EPT Violation VM-Exit > > The above walk of the guest page tables is done in hardware. KVM then does the > following walks in software to retrieve the desired HPA: > > GPA -> [memslots] -> HVA -> [host page tables] -> HPA > > KVM then takes the resulting HPA and shoves it into KVM's shadow page tables, > or when TDP is enabled, the EPT/NPT page tables. When the guest is run with > TDP enabled, GVA->HPA translations look like the following, with all walks done > in hardware. > > GVA -> [guest page tables] -> GPA -> [extended/nested page tables] -> HPA If I understand correctly, the hardware logic of MMU to walk ``GPA -> [extended/nested page tables] -> HPA''[1] should be the same as ``HVA -> [host page tables] -> HPA"[2]. If not true, how does KVM find the correct HPAs when there are EPT violations? [1] Please note that this hardware walk is the last step, which only translates the guest physical address to the host physical address through the four-level nested page table. [2] Please note that this hardware walk assumes translating the HVA to the HPA without virtualization involvement. Thanks, Harry
