[PATCH 0/2] KVM: x86/mmu: Use page-track only for... page tracking

[Sean Christopherson <seanjc@google.com>]

Don't bounce through the page-track notifier when zapping+flushing SPTEs
in response to memslot changes as the need to zap+flush isn't strictly
limited to page-tracking.  With that done, register KVM's notifier on the
first allocation of a shadow root, as KVM's ->track_write() hook is used
only to react to writes to gPTEs.

Aside from avoiding a RETPOLINE on emulated writes, dropping KVM's internal
use will allow removing ->track_flush_slot() altogether once KVM-GT moves
to a different hook[*].  Tracking "flushes" of slots is a poor fit for
KVM-GT's needs as KVM-GT needs to drop its write-protection only when a
memslot change is guaranteed to be committed, whereas the "flush" call is
speculative in the sense that KVM may abort a memslot update after flushing
the original memslot.

https://lore.kernel.org/all/20221108084416.11447-1-yan.y.zhao@intel.com

Sean Christopherson (2):
  KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot
    change
  KVM: x86/mmu: Register page-tracker on first shadow root allocation

 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/mmu/mmu.c          | 24 ++++++++----------------
 arch/x86/kvm/x86.c              |  2 ++
 3 files changed, 11 insertions(+), 16 deletions(-)


base-commit: d663b8a285986072428a6a145e5994bc275df994
-- 
2.38.1.431.g37b22c650d-goog