Hi Dmytro, > -----Original Message----- > From: Dmytro Maluka <dmy@xxxxxxxxxxxx> > Sent: Tuesday, July 26, 2022 7:08 AM > To: Liu, Rong L <rong.l.liu@xxxxxxxxx>; Christopherson,, Sean > <seanjc@xxxxxxxxxx>; Paolo Bonzini <pbonzini@xxxxxxxxxx>; > kvm@xxxxxxxxxxxxxxx > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Ingo Molnar > <mingo@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxxxx>; Dave Hansen > <dave.hansen@xxxxxxxxxxxxxxx>; x86@xxxxxxxxxx; H. Peter Anvin > <hpa@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Eric Auger > <eric.auger@xxxxxxxxxx>; Alex Williamson > <alex.williamson@xxxxxxxxxx>; Zhenyu Wang > <zhenyuw@xxxxxxxxxxxxxxx>; Tomasz Nowicki <tn@xxxxxxxxxxxx>; > Grzegorz Jaszczyk <jaz@xxxxxxxxxxxx>; Dmitry Torokhov > <dtor@xxxxxxxxxx> > Subject: Re: [PATCH 3/3] KVM: irqfd: Postpone resamplefd notify for > oneshot interrupts > > Hi Rong, > > On 7/26/22 01:44, Liu, Rong L wrote: > > Hi Dmytro, > > > >> -----Original Message----- > >> From: Dmytro Maluka <dmy@xxxxxxxxxxxx> > >> Sent: Friday, July 15, 2022 8:59 AM > >> To: Christopherson,, Sean <seanjc@xxxxxxxxxx>; Paolo Bonzini > >> <pbonzini@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx > >> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Ingo Molnar > >> <mingo@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxxxx>; Dave Hansen > >> <dave.hansen@xxxxxxxxxxxxxxx>; x86@xxxxxxxxxx; H. Peter Anvin > >> <hpa@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Eric Auger > >> <eric.auger@xxxxxxxxxx>; Alex Williamson > >> <alex.williamson@xxxxxxxxxx>; Liu, Rong L <rong.l.liu@xxxxxxxxx>; > >> Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>; Tomasz Nowicki > >> <tn@xxxxxxxxxxxx>; Grzegorz Jaszczyk <jaz@xxxxxxxxxxxx>; Dmitry > >> Torokhov <dtor@xxxxxxxxxx>; Dmytro Maluka <dmy@xxxxxxxxxxxx> > >> Subject: [PATCH 3/3] KVM: irqfd: Postpone resamplefd notify for > oneshot > >> interrupts > >> > >> 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. > >> > >> Important notes: > >> > >> 1. It doesn't fix the issue for other archs yet, due to some missing > >> KVM functionality needed by this patch: > >> - calling mask notifiers is implemented for x86 only > >> - irqchip ->is_masked() is implemented for x86 only > >> > >> 2. It introduces an additional spinlock locking in the resample notify > >> path, since we are no longer just traversing an RCU list of irqfds > >> but also updating the resampler state. Hopefully this locking won't > >> noticeably slow down anything for anyone. > >> > > > > Instead of using a spinlock waiting for the unmask event, is it possible > to call > > resampler notify directly when unmask event happens, instead of > calling it on > > EOI? > > In this patch, resampler notify is already called directly when unmask > happens: e.g. with IOAPIC, when the guest unmasks the interrupt by > writing to IOREDTBLx register, ioapic_write_indirect() calls > kvm_fire_mask_notifiers() which calls irqfd_resampler_mask() which > notifies the resampler. On EOI we postpone it just by setting > resampler->pending to true, not by waiting. The spinlock is needed > merely to synchronize reading & updating resampler->pending and > resampler->masked values between possibly concurrently running > instances > of irqfd_resampler_ack() and/or irqfd_resampler_mask(). > > Thanks, > Dmytro > I mean the organization of the code. In current implementation, kvm_ioapic_update_eoi_one() calls kvm_notify_acked_irq(), in your patch, why not call kvm_notify_acked_irq() from ioapic_write_indirect() (roughly at the same place where kvm_fire_mask_notifiers is called), instead of calling it from kvm_ioapic_update_eoi_one, since what your intention here is to notify vfio of the end of interrupt at the event of ioapic unmask, instead of EOI? > > > >> Regarding #2, there may be an alternative solution worth considering: > >> extend KVM irqfd (userspace) API to send mask and unmask > notifications > >> directly to vfio/whatever, in addition to resample notifications, to > >> let vfio check the irq state on its own. There is already locking on > >> vfio side (see e.g. vfio_platform_unmask()), so this way we would > avoid > >> introducing any additional locking. Also such mask/unmask > notifications > >> could be useful for other cases. > >> > >> 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 | 45 > >> +++++++++++++++++++++++++++++++++++++++ > >> 2 files changed, 59 insertions(+) > >> > >> 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 50ddb1d1a7f0..9ff47ac33790 100644 > >> --- a/virt/kvm/eventfd.c > >> +++ b/virt/kvm/eventfd.c > >> @@ -75,6 +75,44 @@ irqfd_resampler_ack(struct > kvm_irq_ack_notifier > >> *kian) > >> kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID, > >> resampler->notifier.gsi, 0, false); > >> > >> + spin_lock(&resampler->lock); > >> + if (resampler->masked) { > >> + resampler->pending = true; > >> + spin_unlock(&resampler->lock); > >> + return; > >> + } > >> + spin_unlock(&resampler->lock); > >> + > >> + 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 > >> +irqfd_resampler_mask(struct kvm_irq_mask_notifier *kimn, bool > >> masked) > >> +{ > >> + struct kvm_kernel_irqfd_resampler *resampler; > >> + struct kvm *kvm; > >> + struct kvm_kernel_irqfd *irqfd; > >> + int idx; > >> + > >> + resampler = container_of(kimn, > >> + struct kvm_kernel_irqfd_resampler, mask_notifier); > >> + kvm = resampler->kvm; > >> + > >> + spin_lock(&resampler->lock); > >> + resampler->masked = masked; > >> + if (masked || !resampler->pending) { > >> + spin_unlock(&resampler->lock); > >> + return; > >> + } > >> + resampler->pending = false; > >> + spin_unlock(&resampler->lock); > >> + > >> idx = srcu_read_lock(&kvm->irq_srcu); > >> > >> list_for_each_entry_srcu(irqfd, &resampler->list, resampler_link, > >> @@ -98,6 +136,8 @@ 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); > >> @@ -367,11 +407,16 @@ 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; > >> + kvm_irq_is_masked(kvm, irqfd->gsi, &resampler- > >>> masked); > >> + spin_lock_init(&resampler->lock); > >> INIT_LIST_HEAD(&resampler->link); > >> > >> list_add(&resampler->link, &kvm->irqfds.resampler_list); > >> kvm_register_irq_ack_notifier(kvm, > >> &resampler->notifier); > >> + kvm_register_irq_mask_notifier(kvm, irqfd->gsi, > >> + &resampler->mask_notifier); > >> irqfd->resampler = resampler; > >> } > >> > >> -- > >> 2.37.0.170.g444d1eabd0-goog > >
