1 files changed, 374 insertions, 0 deletions
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
new file mode 100644
index 000000000000..1b17b12393a8
--- /dev/null
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -0,0 +1,374 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Support KVM gust page tracking
+ *
+ * This feature allows us to track page access in guest. Currently, only
+ * write access is tracked.
+ *
+ * Copyright(C) 2015 Intel Corporation.
+ *
+ * Author:
+ *   Xiao Guangrong <guangrong.xiao@linux.intel.com>
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/lockdep.h>
+#include <linux/kvm_host.h>
+#include <linux/rculist.h>
+
+#include "mmu.h"
+#include "mmu_internal.h"
+#include "page_track.h"
+
+static bool kvm_external_write_tracking_enabled(struct kvm *kvm)
+{
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
+	/*
+	 * Read external_write_tracking_enabled before related pointers.  Pairs
+	 * with the smp_store_release in kvm_page_track_write_tracking_enable().
+	 */
+	return smp_load_acquire(&kvm->arch.external_write_tracking_enabled);
+#else
+	return false;
+#endif
+}
+
+bool kvm_page_track_write_tracking_enabled(struct kvm *kvm)
+{
+	return kvm_external_write_tracking_enabled(kvm) ||
+	       kvm_shadow_root_allocated(kvm) || !tdp_enabled;
+}
+
+void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
+{
+	vfree(slot->arch.gfn_write_track);
+	slot->arch.gfn_write_track = NULL;
+}
+
+static int __kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot,
+						 unsigned long npages)
+{
+	const size_t size = sizeof(*slot->arch.gfn_write_track);
+
+	if (!slot->arch.gfn_write_track)
+		slot->arch.gfn_write_track = __vcalloc(npages, size,
+						       GFP_KERNEL_ACCOUNT);
+
+	return slot->arch.gfn_write_track ? 0 : -ENOMEM;
+}
+
+int kvm_page_track_create_memslot(struct kvm *kvm,
+				  struct kvm_memory_slot *slot,
+				  unsigned long npages)
+{
+	if (!kvm_page_track_write_tracking_enabled(kvm))
+		return 0;
+
+	return __kvm_page_track_write_tracking_alloc(slot, npages);
+}
+
+int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot)
+{
+	return __kvm_page_track_write_tracking_alloc(slot, slot->npages);
+}
+
+static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
+				   short count)
+{
+	int index, val;
+
+	index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
+
+	val = slot->arch.gfn_write_track[index];
+
+	if (WARN_ON_ONCE(val + count < 0 || val + count > USHRT_MAX))
+		return;
+
+	slot->arch.gfn_write_track[index] += count;
+}
+
+void __kvm_write_track_add_gfn(struct kvm *kvm, struct kvm_memory_slot *slot,
+			       gfn_t gfn)
+{
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
+			    srcu_read_lock_held(&kvm->srcu));
+
+	if (KVM_BUG_ON(!kvm_page_track_write_tracking_enabled(kvm), kvm))
+		return;
+
+	update_gfn_write_track(slot, gfn, 1);
+
+	/*
+	 * new track stops large page mapping for the
+	 * tracked page.
+	 */
+	kvm_mmu_gfn_disallow_lpage(slot, gfn);
+
+	if (kvm_mmu_slot_gfn_write_protect(kvm, slot, gfn, PG_LEVEL_4K))
+		kvm_flush_remote_tlbs(kvm);
+}
+
+void __kvm_write_track_remove_gfn(struct kvm *kvm,
+				  struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	lockdep_assert_held_write(&kvm->mmu_lock);
+
+	lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
+			    srcu_read_lock_held(&kvm->srcu));
+
+	if (KVM_BUG_ON(!kvm_page_track_write_tracking_enabled(kvm), kvm))
+		return;
+
+	update_gfn_write_track(slot, gfn, -1);
+
+	/*
+	 * allow large page mapping for the tracked page
+	 * after the tracker is gone.
+	 */
+	kvm_mmu_gfn_allow_lpage(slot, gfn);
+}
+
+/*
+ * check if the corresponding access on the specified guest page is tracked.
+ */
+bool kvm_gfn_is_write_tracked(struct kvm *kvm,
+			      const struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	int index;
+
+	if (!slot)
+		return false;
+
+	if (!kvm_page_track_write_tracking_enabled(kvm))
+		return false;
+
+	index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K);
+	return !!READ_ONCE(slot->arch.gfn_write_track[index]);
+}
+
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
+void kvm_page_track_cleanup(struct kvm *kvm)
+{
+	struct kvm_page_track_notifier_head *head;
+
+	head = &kvm->arch.track_notifier_head;
+	cleanup_srcu_struct(&head->track_srcu);
+}
+
+int kvm_page_track_init(struct kvm *kvm)
+{
+	struct kvm_page_track_notifier_head *head;
+
+	head = &kvm->arch.track_notifier_head;
+	INIT_HLIST_HEAD(&head->track_notifier_list);
+	return init_srcu_struct(&head->track_srcu);
+}
+
+static int kvm_enable_external_write_tracking(struct kvm *kvm)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *slot;
+	int r = 0, i, bkt;
+
+	if (kvm->arch.vm_type == KVM_X86_TDX_VM)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&kvm->slots_arch_lock);
+
+	/*
+	 * Check for *any* write tracking user (not just external users) under
+	 * lock.  This avoids unnecessary work, e.g. if KVM itself is using
+	 * write tracking, or if two external users raced when registering.
+	 */
+	if (kvm_page_track_write_tracking_enabled(kvm))
+		goto out_success;
+
+	for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
+		slots = __kvm_memslots(kvm, i);
+		kvm_for_each_memslot(slot, bkt, slots) {
+			/*
+			 * Intentionally do NOT free allocations on failure to
+			 * avoid having to track which allocations were made
+			 * now versus when the memslot was created.  The
+			 * metadata is guaranteed to be freed when the slot is
+			 * freed, and will be kept/used if userspace retries
+			 * the failed ioctl() instead of killing the VM.
+			 */
+			r = kvm_page_track_write_tracking_alloc(slot);
+			if (r)
+				goto out_unlock;
+		}
+	}
+
+out_success:
+	/*
+	 * Ensure that external_write_tracking_enabled becomes true strictly
+	 * after all the related pointers are set.
+	 */
+	smp_store_release(&kvm->arch.external_write_tracking_enabled, true);
+out_unlock:
+	mutex_unlock(&kvm->slots_arch_lock);
+	return r;
+}
+
+/*
+ * register the notifier so that event interception for the tracked guest
+ * pages can be received.
+ */
+int kvm_page_track_register_notifier(struct kvm *kvm,
+				     struct kvm_page_track_notifier_node *n)
+{
+	struct kvm_page_track_notifier_head *head;
+	int r;
+
+	if (!kvm || kvm->mm != current->mm)
+		return -ESRCH;
+
+	if (!kvm_external_write_tracking_enabled(kvm)) {
+		r = kvm_enable_external_write_tracking(kvm);
+		if (r)
+			return r;
+	}
+
+	kvm_get_kvm(kvm);
+
+	head = &kvm->arch.track_notifier_head;
+
+	write_lock(&kvm->mmu_lock);
+	hlist_add_head_rcu(&n->node, &head->track_notifier_list);
+	write_unlock(&kvm->mmu_lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_page_track_register_notifier);
+
+/*
+ * stop receiving the event interception. It is the opposed operation of
+ * kvm_page_track_register_notifier().
+ */
+void kvm_page_track_unregister_notifier(struct kvm *kvm,
+					struct kvm_page_track_notifier_node *n)
+{
+	struct kvm_page_track_notifier_head *head;
+
+	head = &kvm->arch.track_notifier_head;
+
+	write_lock(&kvm->mmu_lock);
+	hlist_del_rcu(&n->node);
+	write_unlock(&kvm->mmu_lock);
+	synchronize_srcu(&head->track_srcu);
+
+	kvm_put_kvm(kvm);
+}
+EXPORT_SYMBOL_GPL(kvm_page_track_unregister_notifier);
+
+/*
+ * Notify the node that write access is intercepted and write emulation is
+ * finished at this time.
+ *
+ * The node should figure out if the written page is the one that node is
+ * interested in by itself.
+ */
+void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
+{
+	struct kvm_page_track_notifier_head *head;
+	struct kvm_page_track_notifier_node *n;
+	int idx;
+
+	head = &kvm->arch.track_notifier_head;
+
+	if (hlist_empty(&head->track_notifier_list))
+		return;
+
+	idx = srcu_read_lock(&head->track_srcu);
+	hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
+				  srcu_read_lock_held(&head->track_srcu))
+		if (n->track_write)
+			n->track_write(gpa, new, bytes, n);
+	srcu_read_unlock(&head->track_srcu, idx);
+}
+
+/*
+ * Notify external page track nodes that a memory region is being removed from
+ * the VM, e.g. so that users can free any associated metadata.
+ */
+void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	struct kvm_page_track_notifier_head *head;
+	struct kvm_page_track_notifier_node *n;
+	int idx;
+
+	head = &kvm->arch.track_notifier_head;
+
+	if (hlist_empty(&head->track_notifier_list))
+		return;
+
+	idx = srcu_read_lock(&head->track_srcu);
+	hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
+				  srcu_read_lock_held(&head->track_srcu))
+		if (n->track_remove_region)
+			n->track_remove_region(slot->base_gfn, slot->npages, n);
+	srcu_read_unlock(&head->track_srcu, idx);
+}
+
+/*
+ * add guest page to the tracking pool so that corresponding access on that
+ * page will be intercepted.
+ *
+ * @kvm: the guest instance we are interested in.
+ * @gfn: the guest page.
+ */
+int kvm_write_track_add_gfn(struct kvm *kvm, gfn_t gfn)
+{
+	struct kvm_memory_slot *slot;
+	int idx;
+
+	idx = srcu_read_lock(&kvm->srcu);
+
+	slot = gfn_to_memslot(kvm, gfn);
+	if (!slot) {
+		srcu_read_unlock(&kvm->srcu, idx);
+		return -EINVAL;
+	}
+
+	write_lock(&kvm->mmu_lock);
+	__kvm_write_track_add_gfn(kvm, slot, gfn);
+	write_unlock(&kvm->mmu_lock);
+
+	srcu_read_unlock(&kvm->srcu, idx);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
+
+/*
+ * remove the guest page from the tracking pool which stops the interception
+ * of corresponding access on that page.
+ *
+ * @kvm: the guest instance we are interested in.
+ * @gfn: the guest page.
+ */
+int kvm_write_track_remove_gfn(struct kvm *kvm, gfn_t gfn)
+{
+	struct kvm_memory_slot *slot;
+	int idx;
+
+	idx = srcu_read_lock(&kvm->srcu);
+
+	slot = gfn_to_memslot(kvm, gfn);
+	if (!slot) {
+		srcu_read_unlock(&kvm->srcu, idx);
+		return -EINVAL;
+	}
+
+	write_lock(&kvm->mmu_lock);
+	__kvm_write_track_remove_gfn(kvm, slot, gfn);
+	write_unlock(&kvm->mmu_lock);
+
+	srcu_read_unlock(&kvm->srcu, idx);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_write_track_remove_gfn);
+#endif