[PATCH v3 0/8] Lockless Access Tracking for Intel CPUs without EPT A bits

[Junaid Shahid <junaids@google.com>]

Changes from v2:
* Added two patches to refactor mmu_spte_update/clear and add a no_track
  version of mmu_spte_update.
* Ensured that fast_page_fault handles non-write faults to large pages that
  are being access tracked.
* Several minor changes based on code review feedback from v2.

Changes from v1:
* Patch 1 correctly maps to the current codebase by setting the Present bit
  in the page fault error code if any of the Readable, Writeable or Executable
  bits are set in the Exit Qualification.
* Added Patch 5 to update Documentation/virtual/kvm/locking.txt

This patch series implements a lockless access tracking mechanism for KVM
when running on Intel CPUs that do not have EPT A/D bits. 

Currently, KVM tracks accesses on these machines by just clearing the PTEs
and then remapping them when they are accessed again. However, the remapping
requires acquiring the MMU lock in order to lookup the information needed to
construct the PTE. On high core count VMs, this can result in significant MMU
lock contention when running some memory-intesive workloads.

This new mechanism just marks the PTEs as not-present, but keeps all the
information within the PTE instead of clearing it. When the page is accessed
again, the PTE can thus be restored without needing to acquire the MMU lock.

Junaid Shahid (8):
  kvm: x86: mmu: Use symbolic constants for EPT Violation Exit
    Qualifications
  kvm: x86: mmu: Rename spte_is_locklessly_modifiable()
  kvm: x86: mmu: Fast Page Fault path retries
  kvm: x86: mmu: Refactor accessed/dirty checks in mmu_spte_update/clear
  kvm: x86: mmu: Introduce a no-tracking version of mmu_spte_update
  kvm: x86: mmu: Do not use bit 63 for tracking special SPTEs
  kvm: x86: mmu: Lockless access tracking for Intel CPUs without EPT A
    bits.
  kvm: x86: mmu: Update documentation for fast page fault mechanism

 Documentation/virtual/kvm/locking.txt |  31 ++-
 arch/x86/include/asm/kvm_host.h       |  10 +-
 arch/x86/include/asm/vmx.h            |  28 +-
 arch/x86/kvm/mmu.c                    | 464 +++++++++++++++++++++++-----------
 arch/x86/kvm/vmx.c                    |  54 ++--
 arch/x86/kvm/x86.c                    |   2 +-
 6 files changed, 419 insertions(+), 170 deletions(-)

-- 
2.8.0.rc3.226.g39d4020