On Wed, Jun 10, 2020 at 11:01:39AM +0200, Vitaly Kuznetsov wrote: > Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: > > > On 09/06/20 21:10, Vivek Goyal wrote: > >> Hi Vitaly, > >> > >> Have a question about page ready events. > >> > >> Now we deliver PAGE_NOT_PRESENT page faults only if guest is not in > >> kernel mode. So say kernel tried to access a page and we halted cpu. > >> When page is available, we will inject page_ready interrupt. At > >> that time we don't seem to check whether page_not_present was injected > >> or not. > >> > >> IOW, we seem to deliver page_ready irrespective of the fact whether > >> PAGE_NOT_PRESENT was delivered or not. And that means we will be > >> sending page present tokens to guest. Guest will not have a state > >> associated with that token and think that page_not_present has > >> not been delivered yet and allocate an element in hash table for > >> future page_not_present event. And that will lead to memory leak > >> and token conflict etc. > > > > Yes, and this is https://bugzilla.kernel.org/show_bug.cgi?id=208081 > > which I was looking at right today. > > > > The issue isn't related to the interrupt based APF mechanism, right? > 'Page ready' events are always injected (sooner or later). I'll take a > look. > > >> While setting up async pf, should we keep track whether associated > >> page_not_present was delivered to guest or not and deliver page_ready > >> accordingly. > > > > Yes, I think so. > > > > Something like this? (not even compile tested yet): > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 8e8fea13b6c7..68178d29d35c 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1661,7 +1661,7 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm); > void kvm_make_scan_ioapic_request_mask(struct kvm *kvm, > unsigned long *vcpu_bitmap); > > -void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu, > +bool kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu, > struct kvm_async_pf *work); > void kvm_arch_async_page_present(struct kvm_vcpu *vcpu, > struct kvm_async_pf *work); > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c26dd1363151..e1e840df6b69 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -10515,7 +10515,7 @@ bool kvm_can_do_async_pf(struct kvm_vcpu *vcpu) > return kvm_arch_interrupt_allowed(vcpu); > } > > -void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu, > +bool kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu, > struct kvm_async_pf *work) > { > struct x86_exception fault; > @@ -10532,17 +10532,19 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu, > fault.address = work->arch.token; > fault.async_page_fault = true; > kvm_inject_page_fault(vcpu, &fault); > - } else { > - /* > - * It is not possible to deliver a paravirtualized asynchronous > - * page fault, but putting the guest in an artificial halt state > - * can be beneficial nevertheless: if an interrupt arrives, we > - * can deliver it timely and perhaps the guest will schedule > - * another process. When the instruction that triggered a page > - * fault is retried, hopefully the page will be ready in the host. > - */ > - kvm_make_request(KVM_REQ_APF_HALT, vcpu); > + return true; > } > + > + /* > + * It is not possible to deliver a paravirtualized asynchronous > + * page fault, but putting the guest in an artificial halt state > + * can be beneficial nevertheless: if an interrupt arrives, we > + * can deliver it timely and perhaps the guest will schedule > + * another process. When the instruction that triggered a page > + * fault is retried, hopefully the page will be ready in the host. > + */ > + kvm_make_request(KVM_REQ_APF_HALT, vcpu); > + return false; > } > > void kvm_arch_async_page_present(struct kvm_vcpu *vcpu, > @@ -10559,7 +10561,8 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu, > kvm_del_async_pf_gfn(vcpu, work->arch.gfn); > trace_kvm_async_pf_ready(work->arch.token, work->cr2_or_gpa); > > - if (kvm_pv_async_pf_enabled(vcpu) && > + if (work->notpresent_injected && > + kvm_pv_async_pf_enabled(vcpu) && > !apf_put_user_ready(vcpu, work->arch.token)) { > vcpu->arch.apf.pageready_pending = true; > kvm_apic_set_irq(vcpu, &irq, NULL); > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 802b9e2306f0..2456dc5338f8 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -206,6 +206,7 @@ struct kvm_async_pf { > unsigned long addr; > struct kvm_arch_async_pf arch; > bool wakeup_all; > + bool notpresent_injected; > }; > > void kvm_clear_async_pf_completion_queue(struct kvm_vcpu *vcpu); > diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c > index f1e07fae84e9..de28413abefd 100644 > --- a/virt/kvm/async_pf.c > +++ b/virt/kvm/async_pf.c > @@ -189,12 +189,14 @@ int kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > goto retry_sync; > > INIT_WORK(&work->work, async_pf_execute); > - if (!schedule_work(&work->work)) > - goto retry_sync; > > list_add_tail(&work->queue, &vcpu->async_pf.queue); > vcpu->async_pf.queued++; > - kvm_arch_async_page_not_present(vcpu, work); > + work->notpresent_injected = kvm_arch_async_page_not_present(vcpu, work); > + > + /* schedule_work() only fails for already queued works */ > + schedule_work(&work->work); > + > return 1; > retry_sync: This label and associated logic can go away as we are not expecting error from schedule_work(). > kvm_put_kvm(work->vcpu->kvm); > @@ -216,6 +218,7 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu) > return -ENOMEM; > > work->wakeup_all = true; > + work->notpresent_injected = true; This probably is not needed. We already have work->wakeup_all set and this has to be always injected. There is no associated page_not_present event. IMHO, it probably is cleaner to not set it for wake up all events and check work->wakeup_all instead and always inject it. Once you have final patch, I will test it. I have now configured nvdimm device with a file backing the device. I drop the page cache on host and that means any page accessed in guest triggers async pf on host. So I can easily test it. Thanks Vivek
