On Wed, Jul 19, 2023 at 3:35 PM Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > On Tue, Jul 04, 2023 at 04:50:50PM +0900, David Stevens wrote: > > @@ -4451,7 +4461,8 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault > > > > out_unlock: > > write_unlock(&vcpu->kvm->mmu_lock); > > - kvm_release_pfn_clean(fault->pfn); > > + if (fault->is_refcounted_page) > > + kvm_set_page_accessed(pfn_to_page(fault->pfn)); > For a refcounted page, as now KVM puts its ref early in kvm_faultin_pfn(), > should this kvm_set_page_accessed() be placed before unlocking mmu_lock? > > Otherwise, if the user unmaps a region (which triggers kvm_unmap_gfn_range() > with mmu_lock holding for write), and release the page, and if the two > steps happen after checking page_count() in kvm_set_page_accessed() and > before mark_page_accessed(), the latter function may mark accessed to a page > that is released or does not belong to current process. > > Is it true? Yes, good catch. During some testing last week, I actually found this bug thanks to the WARN_ON the first patch in this series added to kvm_is_ad_tracked_page. I'll fix it in the next revision, after Sean gets a chance to comment on the series. Thanks, David
