[PATCH 0/4] KVM, mm: remove the .change_pte() MMU notifier and set_pte_at_notify()

[Paolo Bonzini]

The .change_pte() MMU notifier callback was intended as an optimization
and for this reason it was initially called without a surrounding
mmu_notifier_invalidate_range_{start,end}() pair.  It was only ever
implemented by KVM (which was also the original user of MMU notifiers)
and the rules on when to call set_pte_at_notify() rather than set_pte_at()
have always been pretty obscure.

It may seem a miracle that it has never caused any hard to trigger
bugs, but there's a good reason for that: KVM's implementation has
been nonfunctional for a good part of its existence.  Already in
2012, commit 6bdb913f0a70 ("mm: wrap calls to set_pte_at_notify with
invalidate_range_start and invalidate_range_end", 2012-10-09) changed the
change_pte() callback to occur within an invalidate_range_start/end()
pair; and because KVM unmaps the sPTEs during .invalidate_range_start(),
change_pte() has no hope of finding a sPTE to change.

Therefore, all the code for .change_pte() can be removed from both KVM
and mm/, and set_pte_at_notify() can be replaced with just set_pte_at().

Please review!  Also feel free to take the KVM patches through the mm
tree, as I don't expect any conflicts.

Thanks,

Paolo

Paolo Bonzini (4):
  KVM: delete .change_pte MMU notifier callback
  KVM: remove unused argument of kvm_handle_hva_range()
  mmu_notifier: remove the .change_pte() callback
  mm: replace set_pte_at_notify() with just set_pte_at()

 arch/arm64/kvm/mmu.c                  | 34 -----------------
 arch/loongarch/include/asm/kvm_host.h |  1 -
 arch/loongarch/kvm/mmu.c              | 32 ----------------
 arch/mips/kvm/mmu.c                   | 30 ---------------
 arch/powerpc/include/asm/kvm_ppc.h    |  1 -
 arch/powerpc/kvm/book3s.c             |  5 ---
 arch/powerpc/kvm/book3s.h             |  1 -
 arch/powerpc/kvm/book3s_64_mmu_hv.c   | 12 ------
 arch/powerpc/kvm/book3s_hv.c          |  1 -
 arch/powerpc/kvm/book3s_pr.c          |  7 ----
 arch/powerpc/kvm/e500_mmu_host.c      |  6 ---
 arch/riscv/kvm/mmu.c                  | 20 ----------
 arch/x86/kvm/mmu/mmu.c                | 54 +--------------------------
 arch/x86/kvm/mmu/spte.c               | 16 --------
 arch/x86/kvm/mmu/spte.h               |  2 -
 arch/x86/kvm/mmu/tdp_mmu.c            | 46 -----------------------
 arch/x86/kvm/mmu/tdp_mmu.h            |  1 -
 include/linux/kvm_host.h              |  2 -
 include/linux/mmu_notifier.h          | 44 ----------------------
 include/trace/events/kvm.h            | 15 --------
 kernel/events/uprobes.c               |  5 +--
 mm/ksm.c                              |  4 +-
 mm/memory.c                           |  7 +---
 mm/migrate_device.c                   |  8 +---
 mm/mmu_notifier.c                     | 17 ---------
 virt/kvm/kvm_main.c                   | 50 +------------------------
 26 files changed, 10 insertions(+), 411 deletions(-)

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2.43.0