From: Shaoqin Huang <shaoqin.huang@xxxxxxxxx>
do_unshare() is paired with do_share(), and it's the reverse of the
do_share(), which results in the page sharer take back accessibility of
the shared page for another component which being shared. The page state
become like:
sharer: PAGE_SHARED_OWNED => OWNED
be shared: PAGE_SHARED_BORROWED => NOPAGE
Introduce a do_unshare() helper for safely unsharing a memory region
from one component to another. It will check the page state stored in
pte, and make sure the do_unshare() is paired with do_share(), this will
make the page being correctly take back and can only be accessed by the
page owner after unsharing.
Signed-off-by: Shaoqin Huang <shaoqin.huang@xxxxxxxxx>
---
arch/x86/kvm/vmx/pkvm/hyp/mem_protect.c | 138 ++++++++++++++++++++++++
arch/x86/kvm/vmx/pkvm/hyp/mem_protect.h | 15 +++
2 files changed, 153 insertions(+)
diff --git a/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.c b/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.c
index 987fe172f6a6..092c8b6ea5fe 100644
--- a/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.c
+++ b/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.c
@@ -453,3 +453,141 @@ int __pkvm_host_share_guest(u64 hpa, struct pkvm_pgtable *guest_pgt,
return ret;
}
+
+static int host_request_unshare(const struct pkvm_mem_transition *tx)
+{
+ u64 addr = tx->initiator.host.addr;
+ u64 size = tx->size;
+
+ return __host_check_page_state_range(addr, size, PKVM_PAGE_SHARED_OWNED);
+}
+
+static int guest_ack_unshare(const struct pkvm_mem_transition *tx)
+{
+ u64 addr = tx->completer.guest.addr;
+ u64 size = tx->size;
+
+ return __guest_check_page_state_range(tx->completer.guest.pgt, addr,
+ size, PKVM_PAGE_SHARED_BORROWED);
+}
+
+int check_unshare(const struct pkvm_mem_transition *tx)
+{
+ int ret;
+
+ switch (tx->initiator.id) {
+ case PKVM_ID_HOST:
+ ret = host_request_unshare(tx);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ if (ret)
+ return ret;
+
+ switch (tx->completer.id) {
+ case PKVM_ID_GUEST:
+ ret = guest_ack_unshare(tx);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ return ret;
+}
+
+static int host_initiate_unshare(const struct pkvm_mem_transition *tx)
+{
+ u64 addr = tx->initiator.host.addr;
+ u64 size = tx->size;
+ u64 prot = pkvm_mkstate(tx->initiator.prot, PKVM_PAGE_OWNED);
+
+ return host_ept_create_idmap_locked(addr, size, 0, prot);
+}
+
+static int guest_complete_unshare(const struct pkvm_mem_transition *tx)
+{
+ struct pkvm_pgtable *pgt = tx->completer.guest.pgt;
+ u64 addr = tx->completer.guest.addr;
+ u64 phys = tx->completer.guest.phys;
+ u64 size = tx->size;
+
+ return pkvm_pgtable_unmap_safe(pgt, addr, phys, size);
+}
+
+static int __do_unshare(struct pkvm_mem_transition *tx)
+{
+ int ret;
+
+ switch (tx->initiator.id) {
+ case PKVM_ID_HOST:
+ ret = host_initiate_unshare(tx);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ if (ret)
+ return ret;
+
+ switch (tx->completer.id) {
+ case PKVM_ID_GUEST:
+ ret = guest_complete_unshare(tx);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ return ret;
+}
+
+/*
+ * do_unshare() - The page owner takes back the page access for another
+ * component.
+ *
+ * Initiator: SHARED_OWNED => OWNED
+ * Completer: SHARED_BORROWED => NOPAGE
+ */
+int do_unshare(struct pkvm_mem_transition *share)
+{
+ int ret;
+
+ ret = check_unshare(share);
+ if (ret)
+ return ret;
+
+ return WARN_ON(__do_unshare(share));
+}
+
+int __pkvm_host_unshare_guest(u64 hpa, struct pkvm_pgtable *guest_pgt,
+ u64 gpa, u64 size)
+{
+ int ret;
+ struct pkvm_mem_transition share = {
+ .size = size,
+ .initiator = {
+ .id = PKVM_ID_HOST,
+ .host = {
+ .addr = hpa,
+ },
+ .prot = HOST_EPT_DEF_MEM_PROT,
+ },
+ .completer = {
+ .id = PKVM_ID_GUEST,
+ .guest = {
+ .pgt = guest_pgt,
+ .addr = gpa,
+ .phys = hpa,
+ },
+ },
+ };
+
+ host_ept_lock();
+
+ ret = do_unshare(&share);
+
+ host_ept_unlock();
+
+ return ret;
+}
diff --git a/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.h b/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.h
index 549cc5246620..b004a792b21a 100644
--- a/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.h
+++ b/arch/x86/kvm/vmx/pkvm/hyp/mem_protect.h
@@ -100,4 +100,19 @@ int __pkvm_hyp_donate_host(u64 hpa, u64 size);
int __pkvm_host_share_guest(u64 hpa, struct pkvm_pgtable *guest_pgt,
u64 gpa, u64 size, u64 prot);
+/*
+ * __pkvm_host_unshare_guest() - Host unshare pages that have been shared to guest
+ * previously. Guest will not be able to access these pages.
+ *
+ * @hpa: Start hpa of being shared pages, must be continuous.
+ * @guest_pgt: The guest ept pagetable.
+ * @gpa: Start gpa of shared pages being mapped in guest ept.
+ * @size: The size of pages to be shared.
+ *
+ * Unmap the range [gfn, gfn + nr_pages) in guest ept pagetable. And change
+ * the page state from PAGE_SHARED_BORROWED to PAGE_OWNED in the host ept.
+ */
+int __pkvm_host_unshare_guest(u64 hpa, struct pkvm_pgtable *guest_pgt,
+ u64 gpa, u64 size);
+
#endif
--
2.25.1
