Messages in this thread | | | From | Jim Mattson <> | Date | Fri, 10 Jul 2020 09:30:55 -0700 | Subject | Re: [PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR |
| |
On Fri, Jul 10, 2020 at 8:48 AM Mohammed Gamal <mgamal@redhat.com> wrote: > > When EPT is enabled, KVM does not really look at guest physical > address size. Address bits above maximum physical memory size are reserved. > Because KVM does not look at these guest physical addresses, it currently > effectively supports guest physical address sizes equal to the host. > > This can be problem when having a mixed setup of machines with 5-level page > tables and machines with 4-level page tables, as live migration can change > MAXPHYADDR while the guest runs, which can theoretically introduce bugs.
Huh? Changing MAXPHYADDR while the guest runs should be illegal. Or have I missed some peculiarity of LA57 that makes MAXPHYADDR a dynamic CPUID information field?
> In this patch series we add checks on guest physical addresses in EPT > violation/misconfig and NPF vmexits and if needed inject the proper > page faults in the guest. > > A more subtle issue is when the host MAXPHYADDR is larger than that of the > guest. Page faults caused by reserved bits on the guest won't cause an EPT > violation/NPF and hence we also check guest MAXPHYADDR and add PFERR_RSVD_MASK > error code to the page fault if needed.
| |