Re: [PATCH v3 13/15] KVM: arm64: Implement do_unshare() helper for unsharing memory

[Andrew Walbran <qwandor@google.com>]

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


On Wed, 1 Dec 2021 at 17:05, 'Quentin Perret' via kernel-team
<kernel-team@android.com> wrote:
>
> From: Will Deacon <will@kernel.org>
>
> Tearing down a previously shared memory region results in the borrower
> losing access to the underlying pages and returning them to the "owned"
> state in the owner.
>
> Implement a do_unshare() helper, along the same lines as do_share(), to
> provide this functionality for the host-to-hyp case.
>
> Signed-off-by: Will Deacon <will@kernel.org>
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c | 115 ++++++++++++++++++++++++++
>  1 file changed, 115 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 1282cbd6b9b3..43b25e2de780 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -485,6 +485,16 @@ static int host_request_owned_transition(u64 *completer_addr,
>         return __host_check_page_state_range(addr, size, PKVM_PAGE_OWNED);
>  }
>
> +static int host_request_unshare(u64 *completer_addr,
> +                               const struct pkvm_mem_transition *tx)
> +{
> +       u64 size = tx->nr_pages * PAGE_SIZE;
> +       u64 addr = tx->initiator.addr;
> +
> +       *completer_addr = tx->initiator.host.completer_addr;
> +       return __host_check_page_state_range(addr, size, PKVM_PAGE_SHARED_OWNED);
> +}
> +
>  static int host_initiate_share(u64 *completer_addr,
>                                const struct pkvm_mem_transition *tx)
>  {
> @@ -495,6 +505,16 @@ static int host_initiate_share(u64 *completer_addr,
>         return __host_set_page_state_range(addr, size, PKVM_PAGE_SHARED_OWNED);
>  }
>
> +static int host_initiate_unshare(u64 *completer_addr,
> +                                const struct pkvm_mem_transition *tx)
> +{
> +       u64 size = tx->nr_pages * PAGE_SIZE;
> +       u64 addr = tx->initiator.addr;
> +
> +       *completer_addr = tx->initiator.host.completer_addr;
> +       return __host_set_page_state_range(addr, size, PKVM_PAGE_OWNED);
> +}
> +
>  static enum pkvm_page_state hyp_get_page_state(kvm_pte_t pte)
>  {
>         if (!kvm_pte_valid(pte))
> @@ -535,6 +555,17 @@ static int hyp_ack_share(u64 addr, const struct pkvm_mem_transition *tx,
>         return __hyp_check_page_state_range(addr, size, PKVM_NOPAGE);
>  }
>
> +static int hyp_ack_unshare(u64 addr, const struct pkvm_mem_transition *tx)
> +{
> +       u64 size = tx->nr_pages * PAGE_SIZE;
> +
> +       if (__hyp_ack_skip_pgtable_check(tx))
> +               return 0;
> +
> +       return __hyp_check_page_state_range(addr, size,
> +                                           PKVM_PAGE_SHARED_BORROWED);
> +}
> +
>  static int hyp_complete_share(u64 addr, const struct pkvm_mem_transition *tx,
>                               enum kvm_pgtable_prot perms)
>  {
> @@ -545,6 +576,14 @@ static int hyp_complete_share(u64 addr, const struct pkvm_mem_transition *tx,
>         return pkvm_create_mappings_locked(start, end, prot);
>  }
>
> +static int hyp_complete_unshare(u64 addr, const struct pkvm_mem_transition *tx)
> +{
> +       u64 size = tx->nr_pages * PAGE_SIZE;
> +       int ret = kvm_pgtable_hyp_unmap(&pkvm_pgtable, addr, size);
> +
> +       return (ret != size) ? -EFAULT : 0;
> +}
> +
>  static int check_share(struct pkvm_mem_share *share)
>  {
>         const struct pkvm_mem_transition *tx = &share->tx;
> @@ -621,6 +660,82 @@ static int do_share(struct pkvm_mem_share *share)
>         return WARN_ON(__do_share(share));
>  }
>
> +static int check_unshare(struct pkvm_mem_share *share)
> +{
> +       const struct pkvm_mem_transition *tx = &share->tx;
> +       u64 completer_addr;
> +       int ret;
> +
> +       switch (tx->initiator.id) {
> +       case PKVM_ID_HOST:
> +               ret = host_request_unshare(&completer_addr, tx);
> +               break;
> +       default:
> +               ret = -EINVAL;
> +       }
> +
> +       if (ret)
> +               return ret;
> +
> +       switch (tx->completer.id) {
> +       case PKVM_ID_HYP:
> +               ret = hyp_ack_unshare(completer_addr, tx);
> +               break;
> +       default:
> +               ret = -EINVAL;
> +       }
> +
> +       return ret;
> +}
> +
> +static int __do_unshare(struct pkvm_mem_share *share)
> +{
> +       const struct pkvm_mem_transition *tx = &share->tx;
> +       u64 completer_addr;
> +       int ret;
> +
> +       switch (tx->initiator.id) {
> +       case PKVM_ID_HOST:
> +               ret = host_initiate_unshare(&completer_addr, tx);
> +               break;
> +       default:
> +               ret = -EINVAL;
> +       }
> +
> +       if (ret)
> +               return ret;
> +
> +       switch (tx->completer.id) {
> +       case PKVM_ID_HYP:
> +               ret = hyp_complete_unshare(completer_addr, tx);
> +               break;
> +       default:
> +               ret = -EINVAL;
> +       }
> +
> +       return ret;
> +}
> +
> +/*
> + * do_unshare():
> + *
> + * The page owner revokes access from another component for a range of
> + * pages which were previously shared using do_share().
> + *
> + * Initiator: SHARED_OWNED     => OWNED
> + * Completer: SHARED_BORROWED  => NOPAGE
> + */
> +static int do_unshare(struct pkvm_mem_share *share)
> +{
> +       int ret;
> +
> +       ret = check_unshare(share);
> +       if (ret)
> +               return ret;
> +
> +       return WARN_ON(__do_unshare(share));
> +}
> +
>  int __pkvm_host_share_hyp(u64 pfn)
>  {
>         int ret;
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>
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