[PATCH v6 0/7] KVM: MMU: fast zap all shadow pages

[Xiao Guangrong]

The benchmark and the result can be found at:
http://www.spinics.net/lists/kvm/msg91391.html

Changlog:
V6:
  1): reversely walk active_list to skip the new created pages based
      on the comments from Gleb and Paolo.

  2): completely replace kvm_mmu_zap_all by kvm_mmu_invalidate_all_pages
      based on Gleb's comments.

  3): improve the parameters of kvm_mmu_invalidate_all_pages based on
      Gleb's comments.
 
  4): rename kvm_mmu_invalidate_memslot_pages to kvm_mmu_invalidate_all_pages
  5): rename zap_invalid_pages to kvm_zap_obsolete_pages

V5:
  1): rename is_valid_sp to is_obsolete_sp
  2): use lock-break technique to zap all old pages instead of only pages
      linked on invalid slot's rmap suggested by Marcelo.
  3): trace invalid pages and kvm_mmu_invalidate_memslot_pages()
  4): rename kvm_mmu_invalid_memslot_pages to kvm_mmu_invalidate_memslot_pages
      according to Takuya's comments.

V4:
  1): drop unmapping invalid rmap out of mmu-lock and use lock-break technique
      instead. Thanks to Gleb's comments.

  2): needn't handle invalid-gen pages specially due to page table always
      switched by KVM_REQ_MMU_RELOAD. Thanks to Marcelo's comments.

V3:
  completely redesign the algorithm, please see below.

V2:
  - do not reset n_requested_mmu_pages and n_max_mmu_pages
  - batch free root shadow pages to reduce vcpu notification and mmu-lock
    contention
  - remove the first patch that introduce kvm->arch.mmu_cache since we only
    'memset zero' on hashtable rather than all mmu cache members in this
    version
  - remove unnecessary kvm_reload_remote_mmus after kvm_mmu_zap_all

* Issue
The current kvm_mmu_zap_all is really slow - it is holding mmu-lock to
walk and zap all shadow pages one by one, also it need to zap all guest
page's rmap and all shadow page's parent spte list. Particularly, things
become worse if guest uses more memory or vcpus. It is not good for
scalability.

* Idea
KVM maintains a global mmu invalid generation-number which is stored in
kvm->arch.mmu_valid_gen and every shadow page stores the current global
generation-number into sp->mmu_valid_gen when it is created.

When KVM need zap all shadow pages sptes, it just simply increase the
global generation-number then reload root shadow pages on all vcpus.
Vcpu will create a new shadow page table according to current kvm's
generation-number. It ensures the old pages are not used any more.

Then the invalid-gen pages (sp->mmu_valid_gen != kvm->arch.mmu_valid_gen)
are zapped by using lock-break technique.

Xiao Guangrong (7):
  KVM: MMU: drop unnecessary kvm_reload_remote_mmus
  KVM: MMU: delete shadow page from hash list in
    kvm_mmu_prepare_zap_page
  KVM: MMU: fast invalidate all pages
  KVM: MMU: zap pages in batch
  KVM: x86: use the fast way to invalidate all pages
  KVM: MMU: show mmu_valid_gen in shadow page related tracepoints
  KVM: MMU: add tracepoint for kvm_mmu_invalidate_all_pages

 arch/x86/include/asm/kvm_host.h |    2 +
 arch/x86/kvm/mmu.c              |  115 +++++++++++++++++++++++++++++++++++++--
 arch/x86/kvm/mmu.h              |    1 +
 arch/x86/kvm/mmutrace.h         |   45 ++++++++++++----
 arch/x86/kvm/x86.c              |   11 ++---
 5 files changed, 151 insertions(+), 23 deletions(-)

-- 
1.7.7.6

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