[PATCH 1/3] KVM: x86: add a new page track hook track_remove_slot

[Yan Zhao]

Page track hook track_remove_slot is used to notify users that a slot
has been removed and is called when a slot DELETE/MOVE is about to be
completed.

Users of this hook can drop write protections in the removed slot.

Note:
Since KVM_MR_MOVE currently never actually happens in KVM/QEMU, and has
never been properly supported in the external page track user, we just
use the hook track_remove_slot to notify users of the old slot being
removed.

Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_page_track.h | 11 +++++++++++
 arch/x86/kvm/mmu/page_track.c         | 26 ++++++++++++++++++++++++++
 arch/x86/kvm/x86.c                    |  3 +++
 3 files changed, 40 insertions(+)

diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index eb186bc57f6a..046b024d1813 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -44,6 +44,16 @@ struct kvm_page_track_notifier_node {
 	 */
 	void (*track_flush_slot)(struct kvm *kvm, struct kvm_memory_slot *slot,
 			    struct kvm_page_track_notifier_node *node);
+	/*
+	 * It is called when memory slot is moved or removed
+	 * users can drop write-protection for the pages in that memory slot
+	 *
+	 * @kvm: the kvm where memory slot being moved or removed
+	 * @slot: the memory slot being moved or removed
+	 * @node: this node
+	 */
+	void (*track_remove_slot)(struct kvm *kvm, struct kvm_memory_slot *slot,
+				  struct kvm_page_track_notifier_node *node);
 };
 
 int kvm_page_track_init(struct kvm *kvm);
@@ -76,4 +86,5 @@ kvm_page_track_unregister_notifier(struct kvm *kvm,
 void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
 			  int bytes);
 void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot);
+void kvm_page_track_remove_slot(struct kvm *kvm, struct kvm_memory_slot *slot);
 #endif
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 2e09d1b6249f..4d6bab1d61c9 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -300,3 +300,29 @@ void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
 			n->track_flush_slot(kvm, slot, n);
 	srcu_read_unlock(&head->track_srcu, idx);
 }
+
+/*
+ * Notify the node that memory slot is removed or moved so that it can
+ * drop write-protection for the pages in the memory slot.
+ *
+ * The node should figure out it has any write-protected pages in this slot
+ * by itself.
+ */
+void kvm_page_track_remove_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_slot)
+			n->track_remove_slot(kvm, slot, n);
+	srcu_read_unlock(&head->track_srcu, idx);
+}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 916ebbc81e52..a24a4a2ad1a0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12844,6 +12844,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
+		kvm_page_track_remove_slot(kvm, old);
+
 	if (!kvm->arch.n_requested_mmu_pages &&
 	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
 		unsigned long nr_mmu_pages;
-- 
2.17.1