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

Andrew Walbran
2021-12-10T15:10:31Z

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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