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

Quentin Perret
2021-12-01T17:12:09Z

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