Messages in this thread | | | Date | Mon, 7 Feb 2022 15:35:23 +0100 | Subject | Re: [PATCH 06/23] KVM: MMU: load new PGD once nested two-dimensional paging is initialized | From | Paolo Bonzini <> |
| |
On 2/7/22 14:50, Paolo Bonzini wrote: >>> >> Those checks are just for performance correct (to skip iterating through >> the list of roots)? >> >> Either way, it's probably worth including a Fixes tag below. > > There's no bug because __kvm_mmu_new_pgd is passed a correct new_role. > But it's unnecessarily complex as shown by patches 7 and 9.
root_level is not part of the role, but we're still safe because changing it requires to flip CR0.PG to 0 and back to 1. This calls kvm_mmu_reset_context and unloads all roots, so it's not possible to have a cached PGD with the wrong root level. On the first call the root_level might be incorrect, but then again there's no cached PGD.
(Also, shadow_root_level is either always or never >= PT64_ROOT_4LEVEL, so it's okay unless the guest_mmu was never set up and therefore no cached PGD exists).
Paolo
| |