Messages in this thread | | | Date | Sat, 12 Nov 2022 00:43:07 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH v2 1/3] KVM: x86: add a new page track hook track_remove_slot |
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On Sat, Nov 12, 2022, Yan Zhao wrote: > And I'm also not sure if a slots_arch_lock is required for > kvm_slot_page_track_add_page() and kvm_slot_page_track_remove_page().
It's not required. slots_arch_lock protects interaction between memslot updates mmu_first_shadow_root_alloc(). When CONFIG_KVM_EXTERNAL_WRITE_TRACKING=y, then the mmu_first_shadow_root_alloc() doesn't touch the memslots because everything is pre-allocated:
bool kvm_page_track_write_tracking_enabled(struct kvm *kvm) { return IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING) || !tdp_enabled || kvm_shadow_root_allocated(kvm); }
int kvm_page_track_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot, unsigned long npages) { if (!kvm_page_track_write_tracking_enabled(kvm)) <== always true return 0;
return __kvm_page_track_write_tracking_alloc(slot, npages); }
Though now that you point it out, it's tempting to #ifdef out some of those hooks so that's basically impossible for mmu_first_shadow_root_alloc() to cause problems. Not sure the extra #ideffery would be worth while though.
slots_arch_lock also protects shadow_root_allocated, but that's a KVM-internal detail that isn't relevant to the page-tracking machinery when CONFIG_KVM_EXTERNAL_WRITE_TRACKING=y.
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