On Tuesday 20 Jul 2021 at 11:21:17 (+0100), Marc Zyngier wrote: > On Tue, 20 Jul 2021 11:09:21 +0100, > Quentin Perret <qperret@xxxxxxxxxx> wrote: > > > > On Thursday 15 Jul 2021 at 17:31:46 (+0100), Marc Zyngier wrote: > > > @@ -815,7 +807,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size, > > > .arg = &map_data, > > > }; > > > > > > - if (owner_id > KVM_MAX_OWNER_ID) > > > + if (!annotation || (annotation & PTE_VALID)) > > > return -EINVAL; > > > > Why do you consider annotation==0 invalid? The assumption so far has > > been that the owner_id for the host is 0, so annotating a range with 0s > > should be a valid operation -- this will be required when e.g. > > transferring ownership of a page back to the host. > > How do you then distinguish it from an empty entry that doesn't map to > anything at all? You don't, but that's beauty of it :) The host starts with a PGD full of zeroes, which in terms of ownership means that it owns the entire (I)PA space. And it loses ownership of a page only when we explicitly annotate it with an owner id != 0.
