Re: [PATCH v3 12/21] KVM: arm64: Add helpers to tag shared pages in SW bits

Fuad Tabba
2021-08-02T10:31:05Z

Hi Quentin,

On Thu, Jul 29, 2021 at 3:28 PM Quentin Perret <qperret@google.com> wrote:
>
> We will soon start annotating shared pages in page-tables in nVHE
> protected mode. Define all the states in which a page can be (owned,
> shared and owned, shared and borrowed), and provide helpers allowing to
> convert this into SW bits annotations using the matching prot
> attributes.
>
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
> arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 26 +++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> index 9c227d87c36d..ae355bfd8c01 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -12,6 +12,32 @@
> #include <asm/virt.h>
> #include <nvhe/spinlock.h>
>
> +/*
> + * SW bits 0-1 are reserved to track the memory ownership state of each page:
> + * 00: The page is owned solely by the page-table owner.

nit: solely -> exclusively, because "exclusive" is the more common
term in context of shared resources

> + * 01: The page is owned by the page-table owner, but is shared
> + * with another entity.
> + * 10: The page is shared with, but not owned by the page-table owner.
> + * 11: Reserved for future use (lending).
> + */
> +enum pkvm_page_state {
> + PKVM_PAGE_OWNED = 0ULL,
> + PKVM_PAGE_SHARED_OWNED = KVM_PGTABLE_PROT_SW0,
> + PKVM_PAGE_SHARED_BORROWED = KVM_PGTABLE_PROT_SW1,
> +};
> +
> +#define PKVM_PAGE_STATE_PROT_MASK (KVM_PGTABLE_PROT_SW0 | KVM_PGTABLE_PROT_SW1)
> +static inline enum kvm_pgtable_prot pkvm_mkstate(enum kvm_pgtable_prot prot,
> + enum pkvm_page_state state)
> +{
> + return (prot & ~PKVM_PAGE_STATE_PROT_MASK) | state;
> +}
> +
> +static inline enum pkvm_page_state pkvm_getstate(enum kvm_pgtable_prot prot)
> +{
> + return prot & PKVM_PAGE_STATE_PROT_MASK;
> +}
> +

I think that this encoding is pretty neat and easy to follow.

Reviewed-by: Fuad Tabba <tabba@google.com>

Thanks,
/fuad

> struct host_kvm {
> struct kvm_arch arch;
> struct kvm_pgtable pgt;
> --
> 2.32.0.432.gabb21c7263-goog
>