Messages in this thread | | | Date | Mon, 2 Aug 2021 18:30:13 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH 1/2] KVM: Block memslot updates across range_start() and range_end() |
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On Tue, Jul 27, 2021, Paolo Bonzini wrote: > @@ -764,8 +769,9 @@ static inline struct kvm_memslots *__kvm_memslots(struct kvm *kvm, int as_id) > { > as_id = array_index_nospec(as_id, KVM_ADDRESS_SPACE_NUM); > return srcu_dereference_check(kvm->memslots[as_id], &kvm->srcu, > - lockdep_is_held(&kvm->slots_lock) || > - !refcount_read(&kvm->users_count)); > + lockdep_is_held(&kvm->slots_lock) || > + READ_ONCE(kvm->mn_active_invalidate_count) ||
Hmm, I'm not sure we should add mn_active_invalidate_count as an exception to holding kvm->srcu. It made sense in original (flawed) approach because the exception was a locked_is_held() check, i.e. it was verifying the the current task holds the lock. With mn_active_invalidate_count, this only verifies that there's an invalidation in-progress, it doesn't verify that this task/CPU is the one doing the invalidation.
Since __kvm_handle_hva_range() takes SRCU for read, maybe it's best omit this?
> + !refcount_read(&kvm->users_count)); > } > > static inline struct kvm_memslots *kvm_memslots(struct kvm *kvm)
...
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 5cc79373827f..c64a7de60846 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -605,10 +605,8 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn, > > /* > * .change_pte() must be surrounded by .invalidate_range_{start,end}(),
Nit, the comma can be switch to a period. The next patch starts a new sentence, so it would be correct even in the long term.
> - * and so always runs with an elevated notifier count. This obviates > - * the need to bump the sequence count. > */ > - WARN_ON_ONCE(!kvm->mmu_notifier_count); > + WARN_ON_ONCE(!READ_ONCE(kvm->mn_active_invalidate_count)); > > kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn); > }
Nits aside,
Reviewed-by: Sean Christopherson <seanjc@google.com>
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