[PATCH 1/3] KVM: arm64: add a hypercall for disowning pages

[Quentin Perret]

Hi Peter,

On Wednesday 22 Jun 2022 at 19:19:24 (-0700), Peter Collingbourne wrote:
> @@ -677,9 +678,9 @@ static bool stage2_pte_is_counted(kvm_pte_t pte)
>  	/*
>  	 * The refcount tracks valid entries as well as invalid entries if they
>  	 * encode ownership of a page to another entity than the page-table
> -	 * owner, whose id is 0.
> +	 * owner, whose id is 0, or NOBODY, which does not correspond to a page-table.
>  	 */
> -	return !!pte;
> +	return !!pte && pte != kvm_init_invalid_leaf_owner(PKVM_ID_NOBODY);
>  }

I'm not sure to understand this part? By not refcounting the PTEs that
are annotated with PKVM_ID_NOBODY, the page-table page that contains
them may be freed at some point. And when that happens, I don't see how
the hypervisor will remember to block host accesses to the disowned
pages.

Cheers,
Quentin