| Subject | Re: [RFC PATCH v2 16/69] KVM: x86/mmu: Zap only leaf SPTEs for deleted/moved memslot by default | From | Paolo Bonzini <> | Date | Tue, 6 Jul 2021 15:44:22 +0200 |
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On 03/07/21 00:04, isaku.yamahata@intel.com wrote: > From: Sean Christopherson <sean.j.christopherson@intel.com> > > Zap only leaf SPTEs when deleting/moving a memslot by default, and add a > module param to allow reverting to the old behavior of zapping all SPTEs > at all levels and memslots when any memslot is updated. > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com> > --- > arch/x86/kvm/mmu/mmu.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 8d5876dfc6b7..5b8a640f8042 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -85,6 +85,9 @@ __MODULE_PARM_TYPE(nx_huge_pages_recovery_ratio, "uint"); > static bool __read_mostly force_flush_and_sync_on_reuse; > module_param_named(flush_on_reuse, force_flush_and_sync_on_reuse, bool, 0644); > > +static bool __read_mostly memslot_update_zap_all; > +module_param(memslot_update_zap_all, bool, 0444); > + > /* > * When setting this variable to true it enables Two-Dimensional-Paging > * where the hardware walks 2 page tables: > @@ -5480,11 +5483,27 @@ static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm) > return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages)); > } > > +static void kvm_mmu_zap_memslot(struct kvm *kvm, struct kvm_memory_slot *slot) > +{ > + /* > + * Zapping non-leaf SPTEs, a.k.a. not-last SPTEs, isn't required, worst > + * case scenario we'll have unused shadow pages lying around until they > + * are recycled due to age or when the VM is destroyed. > + */ > + write_lock(&kvm->mmu_lock); > + slot_handle_level(kvm, slot, kvm_zap_rmapp, PG_LEVEL_4K, > + KVM_MAX_HUGEPAGE_LEVEL, true); > + write_unlock(&kvm->mmu_lock); > +} > + > static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm, > struct kvm_memory_slot *slot, > struct kvm_page_track_notifier_node *node) > { > - kvm_mmu_zap_all_fast(kvm); > + if (memslot_update_zap_all) > + kvm_mmu_zap_all_fast(kvm); > + else > + kvm_mmu_zap_memslot(kvm, slot); > } > > void kvm_mmu_init_vm(struct kvm *kvm) >
This is the old patch that broke VFIO for some unknown reason. The commit message should at least say why memslot_update_zap_all is not true by default. Also, IIUC the bug still there with NX hugepage splits disabled, but what if the TDP MMU is enabled?
Paolo
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