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
