Re: [PATCH 07/11] KVM: page track: add notifier support

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On 12/16/2015 01:53 PM, Jike Song wrote:
On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
Notifier list is introduced so that any node wants to receive the track
event can register to the list

Two APIs are introduced here:
- kvm_page_track_register_notifier(): register the notifier to receive
   track event

- kvm_page_track_unregister_notifier(): stop receiving track event by
   unregister the notifier

The callback, node->track_write() is called when a write access on the
write tracked page happens

Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
---
  arch/x86/include/asm/kvm_host.h       |  1 +
  arch/x86/include/asm/kvm_page_track.h | 39 ++++++++++++++++++++
  arch/x86/kvm/page_track.c             | 67 +++++++++++++++++++++++++++++++++++
  arch/x86/kvm/x86.c                    |  4 +++
  4 files changed, 111 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index afff1f1..0f7b940 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -658,6 +658,7 @@ struct kvm_arch {
       */
      struct list_head active_mmu_pages;
      struct list_head zapped_obsolete_pages;
+    struct kvm_page_track_notifier_head track_notifier_head;

      struct list_head assigned_dev_head;
      struct iommu_domain *iommu_domain;
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index f223201..6744234 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -6,6 +6,36 @@ enum kvm_page_track_mode {
      KVM_PAGE_TRACK_MAX,
  };

+/*
+ * The notifier represented by @kvm_page_track_notifier_node is linked into
+ * the head which will be notified when guest is triggering the track event.
+ *
+ * Write access on the head is protected by kvm->mmu_lock, read access
+ * is protected by track_srcu.
+ */
+struct kvm_page_track_notifier_head {
+    struct srcu_struct track_srcu;
+    struct hlist_head track_notifier_list;
+};
+
+struct kvm_page_track_notifier_node {
+    struct hlist_node node;
+
+    /*
+     * It is called when guest is writing the write-tracked page
+     * and write emulation is finished at that time.
+     *
+     * @vcpu: the vcpu where the write access happened.
+     * @gpa: the physical address written by guest.
+     * @new: the data was written to the address.
+     * @bytes: the written length.
+     */
+    void (*track_write)(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
+                int bytes);

Sir, is it possible to make this non-void? as you described below, the
callback may find this gpa isn't the page being tracked, so it probably
want to return something to indicate: not my business, continue :)

Currently the return value is useless and it is not ABI so we can extend
it if it is needed in the future.

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