Re: [PATCH v3 09/15] KVM: arm64: Extend pkvm_page_state enumeration to handle absent pages

[Andrew Walbran <qwandor@google.com>]

On Wed, 1 Dec 2021 at 17:04, 'Quentin Perret' via kernel-team
<kernel-team@android.com> wrote:
>
> From: Will Deacon <will@kernel.org>
>
> Explicitly name the combination of SW0 | SW1 as reserved in the pte and
> introduce a new PKVM_NOPAGE meta-state which, although not directly
> stored in the software bits of the pte, can be used to represent an
> entry for which there is no underlying page. This is distinct from an
> invalid pte, as stage-2 identity mappings for the host are created
> lazily and so an invalid pte there is the same as a valid mapping for
> the purposes of ownership information.
>
> This state will be used for permission checking during page transitions
> in later patches.
>
> Signed-off-by: Will Deacon <will@kernel.org>
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> index b58c910babaf..56445586c755 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -24,6 +24,11 @@ enum pkvm_page_state {
>         PKVM_PAGE_OWNED                 = 0ULL,
>         PKVM_PAGE_SHARED_OWNED          = KVM_PGTABLE_PROT_SW0,
>         PKVM_PAGE_SHARED_BORROWED       = KVM_PGTABLE_PROT_SW1,
> +       __PKVM_PAGE_RESERVED            = KVM_PGTABLE_PROT_SW0 |
> +                                         KVM_PGTABLE_PROT_SW1,
> +
> +       /* Meta-states which aren't encoded directly in the PTE's SW bits */
> +       PKVM_NOPAGE,
>  };
>
>  #define PKVM_PAGE_STATE_PROT_MASK      (KVM_PGTABLE_PROT_SW0 | KVM_PGTABLE_PROT_SW1)
> --
> 2.34.0.rc2.393.gf8c9666880-goog

Reviewed-by: Andrew Walbran <qwandor@google.com>