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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id j10sm13563971pfd.200.2021.08.02.11.30.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Aug 2021 11:30:17 -0700 (PDT) Date: Mon, 2 Aug 2021 18:30:13 +0000 From: Sean Christopherson To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: Block memslot updates across range_start() and range_end() Message-ID: References: <20210727171808.1645060-1-pbonzini@redhat.com> <20210727171808.1645060-2-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210727171808.1645060-2-pbonzini@redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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