[PATCH 1/2] KVM: Keep track of the number of memslots with dirty logging enabled

[David Matlack <dmatlack@google.com>]

Add a new field to struct kvm that keeps track of the number of memslots
with dirty logging enabled. This will be used in a future commit to
cheaply check if any memslot is doing dirty logging.

Signed-off-by: David Matlack <dmatlack@google.com>
---
 include/linux/kvm_host.h |  2 ++
 virt/kvm/kvm_main.c      | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 32f259fa5801..25ed8c1725ff 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -709,6 +709,8 @@ struct kvm {
 	struct kvm_memslots __memslots[KVM_ADDRESS_SPACE_NUM][2];
 	/* The current active memslot set for each address space */
 	struct kvm_memslots __rcu *memslots[KVM_ADDRESS_SPACE_NUM];
+	/* The number of memslots with dirty logging enabled. */
+	int nr_memslots_dirty_logging;
 	struct xarray vcpu_array;
 
 	/* Used to wait for completion of MMU notifiers.  */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e30f1b4ecfa5..57e4406005cd 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1641,6 +1641,9 @@ static void kvm_commit_memory_region(struct kvm *kvm,
 				     const struct kvm_memory_slot *new,
 				     enum kvm_mr_change change)
 {
+	int old_flags = old ? old->flags : 0;
+	int new_flags = new ? new->flags : 0;
+
 	/*
 	 * Update the total number of memslot pages before calling the arch
 	 * hook so that architectures can consume the result directly.
@@ -1650,6 +1653,13 @@ static void kvm_commit_memory_region(struct kvm *kvm,
 	else if (change == KVM_MR_CREATE)
 		kvm->nr_memslot_pages += new->npages;
 
+	if ((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES) {
+		if (new_flags & KVM_MEM_LOG_DIRTY_PAGES)
+			kvm->nr_memslots_dirty_logging++;
+		else
+			kvm->nr_memslots_dirty_logging--;
+	}
+
 	kvm_arch_commit_memory_region(kvm, old, new, change);
 
 	switch (change) {
-- 
2.38.1.273.g43a17bfeac-goog