On Fri, 05 Apr 2024 12:58:11 +0100,
Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> 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(-)
>
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
M.
--
Without deviation from the norm, progress is not possible.
