On Mon, Mar 15, 2021 at 02:35:29PM +0000, Quentin Perret wrote:
> As the host stage 2 will be identity mapped, all the .hyp memory regions
> and/or memory pages donated to protected guestis will have to marked
> invalid in the host stage 2 page-table. At the same time, the hypervisor
> will need a way to track the ownership of each physical page to ensure
> memory sharing or donation between entities (host, guests, hypervisor) is
> legal.
>
> In order to enable this tracking at EL2, let's use the host stage 2
> page-table itself. The idea is to use the top bits of invalid mappings
> to store the unique identifier of the page owner. The page-table owner
> (the host) gets identifier 0 such that, at boot time, it owns the entire
> IPA space as the pgd starts zeroed.
>
> Provide kvm_pgtable_stage2_set_owner() which allows to modify the
> ownership of pages in the host stage 2. It re-uses most of the map()
> logic, but ends up creating invalid mappings instead. This impacts
> how we do refcount as we now need to count invalid mappings when they
> are used for ownership tracking.
>
> Signed-off-by: Quentin Perret <qper...@google.com>
> ---
> arch/arm64/include/asm/kvm_pgtable.h | 21 +++++
> arch/arm64/kvm/hyp/pgtable.c | 127 ++++++++++++++++++++++-----
> 2 files changed, 124 insertions(+), 24 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h
> b/arch/arm64/include/asm/kvm_pgtable.h
> index 4ae19247837b..683e96abdc24 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -238,6 +238,27 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64
> addr, u64 size,
> u64 phys, enum kvm_pgtable_prot prot,
> void *mc);
>
> +/**
> + * kvm_pgtable_stage2_set_owner() - Annotate invalid mappings with metadata
> + * encoding the ownership of a page in the
> + * IPA space.
The function does more than this, though, as it will also go ahead and unmap
existing valid mappings which I think should be mentioned here, no?
> +int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size,
> + void *mc, u8 owner_id)
> +{
> + int ret;
> + struct stage2_map_data map_data = {
> + .phys = KVM_PHYS_INVALID,
> + .mmu = pgt->mmu,
> + .memcache = mc,
> + .mm_ops = pgt->mm_ops,
> + .owner_id = owner_id,
> + };
> + struct kvm_pgtable_walker walker = {
> + .cb = stage2_map_walker,
> + .flags = KVM_PGTABLE_WALK_TABLE_PRE |
> + KVM_PGTABLE_WALK_LEAF |
> + KVM_PGTABLE_WALK_TABLE_POST,
> + .arg = &map_data,
> + };
> +
> + if (owner_id > KVM_MAX_OWNER_ID)
> + return -EINVAL;
> +
> + ret = kvm_pgtable_walk(pgt, addr, size, &walker);
> + dsb(ishst);
Why is the DSB needed here? afaict, we only ever unmap a valid entry (which
will have a DSB as part of the TLBI sequence) or we update the owner for an
existing invalid entry, in which case the walker doesn't care.
Will
