Hi Dmytro, On 8/5/22 21:39, Dmytro Maluka wrote: > The existing KVM mechanism for forwarding of level-triggered interrupts > using resample eventfd doesn't work quite correctly in the case of > interrupts that are handled in a Linux guest as oneshot interrupts > (IRQF_ONESHOT). Such an interrupt is acked to the device in its > threaded irq handler, i.e. later than it is acked to the interrupt > controller (EOI at the end of hardirq), not earlier. > > Linux keeps such interrupt masked until its threaded handler finishes, > to prevent the EOI from re-asserting an unacknowledged interrupt. > However, with KVM + vfio (or whatever is listening on the resamplefd) > we don't check that the interrupt is still masked in the guest at the > moment of EOI. Resamplefd is notified regardless, so vfio prematurely > unmasks the host physical IRQ, thus a new (unwanted) physical interrupt > is generated in the host and queued for injection to the guest. > > The fact that the virtual IRQ is still masked doesn't prevent this new > physical IRQ from being propagated to the guest, because: > > 1. It is not guaranteed that the vIRQ will remain masked by the time > when vfio signals the trigger eventfd. > 2. KVM marks this IRQ as pending (e.g. setting its bit in the virtual > IRR register of IOAPIC on x86), so after the vIRQ is unmasked, this > new pending interrupt is injected by KVM to the guest anyway. > > There are observed at least 2 user-visible issues caused by those > extra erroneous pending interrupts for oneshot irq in the guest: > > 1. System suspend aborted due to a pending wakeup interrupt from > ChromeOS EC (drivers/platform/chrome/cros_ec.c). > 2. Annoying "invalid report id data" errors from ELAN0000 touchpad > (drivers/input/mouse/elan_i2c_core.c), flooding the guest dmesg > every time the touchpad is touched. > > This patch fixes the issue on x86 by checking if the interrupt is > unmasked when we receive irq ack (EOI) and, in case if it's masked, > postponing resamplefd notify until the guest unmasks it. > > It doesn't fix the issue for other archs yet, since it relies on KVM > irq mask notifiers functionality which currently works only on x86. > On other archs we can register mask notifiers but they are never called. > So on other archs resampler->masked is always false, so the behavior is > the same as before this patch. > > Link: https://lore.kernel.org/kvm/31420943-8c5f-125c-a5ee-d2fde2700083@xxxxxxxxxxxx/ > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > Signed-off-by: Dmytro Maluka <dmy@xxxxxxxxxxxx> > --- > include/linux/kvm_irqfd.h | 14 ++++++++++ > virt/kvm/eventfd.c | 56 +++++++++++++++++++++++++++++++++++---- > 2 files changed, 65 insertions(+), 5 deletions(-) > > diff --git a/include/linux/kvm_irqfd.h b/include/linux/kvm_irqfd.h > index dac047abdba7..01754a1abb9e 100644 > --- a/include/linux/kvm_irqfd.h > +++ b/include/linux/kvm_irqfd.h > @@ -19,6 +19,16 @@ > * resamplefd. All resamplers on the same gsi are de-asserted > * together, so we don't need to track the state of each individual > * user. We can also therefore share the same irq source ID. > + * > + * A special case is when the interrupt is still masked at the moment > + * an irq ack is received. That likely means that the interrupt has > + * been acknowledged to the interrupt controller but not acknowledged > + * to the device yet, e.g. it might be a Linux guest's threaded > + * oneshot interrupt (IRQF_ONESHOT). In this case notifying through > + * resamplefd is postponed until the guest unmasks the interrupt, > + * which is detected through the irq mask notifier. This prevents > + * erroneous extra interrupts caused by premature re-assert of an > + * unacknowledged interrupt by the resamplefd listener. > */ > struct kvm_kernel_irqfd_resampler { > struct kvm *kvm; > @@ -28,6 +38,10 @@ struct kvm_kernel_irqfd_resampler { > */ > struct list_head list; > struct kvm_irq_ack_notifier notifier; > + struct kvm_irq_mask_notifier mask_notifier; > + bool masked; > + bool pending; > + spinlock_t lock; > /* > * Entry in list of kvm->irqfd.resampler_list. Use for sharing > * resamplers among irqfds on the same gsi. > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 3007d956b626..f98dcce3959c 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -67,6 +67,7 @@ irqfd_resampler_ack(struct kvm_irq_ack_notifier *kian) > struct kvm *kvm; > struct kvm_kernel_irqfd *irqfd; > int idx; > + bool notify = true; > > resampler = container_of(kian, > struct kvm_kernel_irqfd_resampler, notifier); > @@ -75,13 +76,52 @@ irqfd_resampler_ack(struct kvm_irq_ack_notifier *kian) > kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID, > resampler->notifier.gsi, 0, false); > > - idx = srcu_read_lock(&kvm->irq_srcu); > + spin_lock(&resampler->lock); > + if (resampler->masked) { > + notify = false; > + resampler->pending = true; > + } > + spin_unlock(&resampler->lock); > + > + if (notify) { > + idx = srcu_read_lock(&kvm->irq_srcu); > > - list_for_each_entry_srcu(irqfd, &resampler->list, resampler_link, > - srcu_read_lock_held(&kvm->irq_srcu)) > - eventfd_signal(irqfd->resamplefd, 1); > + list_for_each_entry_srcu(irqfd, &resampler->list, resampler_link, > + srcu_read_lock_held(&kvm->irq_srcu)) > + eventfd_signal(irqfd->resamplefd, 1); nit: you may introduce a helper for above code as the code is duplicated. > > - srcu_read_unlock(&kvm->irq_srcu, idx); > + srcu_read_unlock(&kvm->irq_srcu, idx); > + } > +} > + > +static void irqfd_resampler_mask_notify(struct kvm_irq_mask_notifier *kimn, > + bool masked) > +{ > + struct kvm_kernel_irqfd_resampler *resampler; > + struct kvm *kvm; > + struct kvm_kernel_irqfd *irqfd; > + int idx; > + bool notify; > + > + resampler = container_of(kimn, > + struct kvm_kernel_irqfd_resampler, mask_notifier); > + kvm = resampler->kvm; > + > + spin_lock(&resampler->lock); > + notify = !masked && resampler->pending; > + resampler->masked = masked; > + resampler->pending = false; > + spin_unlock(&resampler->lock); > + > + if (notify) { > + idx = srcu_read_lock(&kvm->irq_srcu); > + > + list_for_each_entry_srcu(irqfd, &resampler->list, resampler_link, > + srcu_read_lock_held(&kvm->irq_srcu)) > + eventfd_signal(irqfd->resamplefd, 1); > + > + srcu_read_unlock(&kvm->irq_srcu, idx); > + } > } > > static void > @@ -98,6 +138,8 @@ irqfd_resampler_shutdown(struct kvm_kernel_irqfd *irqfd) > if (list_empty(&resampler->list)) { > list_del(&resampler->link); > kvm_unregister_irq_ack_notifier(kvm, &resampler->notifier); > + kvm_unregister_irq_mask_notifier(kvm, resampler->mask_notifier.irq, > + &resampler->mask_notifier); > kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID, > resampler->notifier.gsi, 0, false); > kfree(resampler); > @@ -367,9 +409,13 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > INIT_LIST_HEAD(&resampler->list); > resampler->notifier.gsi = irqfd->gsi; > resampler->notifier.irq_acked = irqfd_resampler_ack; > + resampler->mask_notifier.func = irqfd_resampler_mask_notify; > + spin_lock_init(&resampler->lock); > INIT_LIST_HEAD(&resampler->link); > > list_add(&resampler->link, &kvm->irqfds.resampler_list); > + kvm_register_and_fire_irq_mask_notifier(kvm, irqfd->gsi, > + &resampler->mask_notifier); > kvm_register_irq_ack_notifier(kvm, > &resampler->notifier); > irqfd->resampler = resampler; Adding Marc in CC Thanks Eric
