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 > >> 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 >
