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: 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; INIT_LIST_HEAD(&work->queue); /* for list_del to work */ spin_lock(&vcpu->async_pf.lock); -- Vitaly
