On Tue, Oct 13, 2020 at 12:30:39AM -0400, harry harry wrote: > Hi Sean, > > Thank you very much for your thorough explanations. Please see my > inline replies 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 > > Do you mean that GPAs are different from their corresponding HVAs when > KVM does the walks (as you said above) in software? What do you mean by "different"? GPAs and HVAs are two completely different address spaces.
