This patchset introduces the feature which allows us to track page
access in guest. Currently, only write access tracking is implemented
in this version.

Four APIs are introduces:
- kvm_page_track_add_page(kvm, gfn, mode), single guest page @gfn is
  added into the track pool of the guest instance represented by @kvm,
  @mode specifies which kind of access on the @gfn is tracked
- kvm_page_track_remove_page(kvm, gfn, mode), is the opposed operation
  of kvm_page_track_add_page() which removes @gfn from the tracking pool.
  gfn is no tracked after its last user is gone

- kvm_page_track_register_notifier(kvm, n), register a notifier so that
  the event triggered by page tracking will be received, at that time,
  the callback of n->track_write() will be called

- kvm_page_track_unregister_notifier(kvm, n), does the opposed operation
  of kvm_page_track_register_notifier(), which unlinks the notifier and
  stops receiving the tracked event

The first user of page track is non-leaf shadow page tables as they are
always write protected. It also gains performance improvement because
page track speeds up page fault handler for the tracked pages. The
performance result of kernel building is as followings:

   before           after
real 461.63       real 455.48
user 4529.55      user 4557.88
sys 1995.39       sys 1922.57

Furthermore, it is the infrastructure of other kind of shadow page table,
such as GPU shadow page table introduced in KVMGT (1) and native nested

This patch can be divided into two parts:
- patch 1 ~ patch 7, implement page tracking
- others patches apply page tracking to non-leaf shadow page table


Xiao Guangrong (11):
  KVM: MMU: rename has_wrprotected_page to mmu_gfn_lpage_is_disallowed
  KVM: MMU: introduce kvm_mmu_gfn_{allow,disallow}_lpage
  KVM: MMU: introduce kvm_mmu_slot_gfn_write_protect
  KVM: page track: add the framework of guest page tracking
  KVM: page track: introduce kvm_page_track_{add,remove}_page
  KVM: MMU: let page fault handler be aware tracked page
  KVM: page track: add notifier support
  KVM: MMU: use page track for non-leaf shadow pages
  KVM: MMU: simplify mmu_need_write_protect
  KVM: MMU: clear write-flooding on the fast path of tracked page
  KVM: MMU: apply page track notifier

 Documentation/virtual/kvm/mmu.txt     |   6 +-
 arch/x86/include/asm/kvm_host.h       |  12 +-
 arch/x86/include/asm/kvm_page_track.h |  67 +++++++++
 arch/x86/kvm/Makefile                 |   3 +-
 arch/x86/kvm/mmu.c                    | 199 +++++++++++++++++++--------
 arch/x86/kvm/mmu.h                    |   5 +
 arch/x86/kvm/page_track.c             | 252 ++++++++++++++++++++++++++++++++++
 arch/x86/kvm/paging_tmpl.h            |   5 +
 arch/x86/kvm/x86.c                    |  27 ++--
 9 files changed, 504 insertions(+), 72 deletions(-)
 create mode 100644 arch/x86/include/asm/kvm_page_track.h
 create mode 100644 arch/x86/kvm/page_track.c


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