KVM_REQ_MMU_RELOAD is raised after kvm->arch.mmu_valid_gen is fixed (of
course, otherwise the other CPU might just not see any obsoleted page
from the legacy MMU), therefore any check on KVM_REQ_MMU_RELOAD is just
advisory.
I disagree. IMO, KVM should not be installing SPTEs into obsolete shadow pages,
which is what continuing on allows. I don't _think_ it's problematic, but I do
think it's wrong.
[...] Eh, for all intents and purposes, KVM_REQ_MMU_RELOAD very much says
special roots are obsolete. The root will be unloaded, i.e. will no
longer be used, i.e. is obsolete.
The other way to check for an invalid special root would be to treat
it as obsolete if any of its children in entries 0-3 are present and
obsolete. That would be more precise, but it provides no benefit
given KVM's current implementation.
I'm not completely opposed to doing nothing, but I do think it's
silly to continue on knowing that the work done by the page fault is
all but gauranteed to be useless.