On Tue, 20 Jul 2021 11:38:17 +0100, Quentin Perret <qperret@xxxxxxxxxx> wrote: > > 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. Right. But this scheme doesn't apply to the guests, does it? Don't we need something that is non-null to preserve the table refcounting? Thanks, M. -- Without deviation from the norm, progress is not possible.
