Hi Rong, On 8/10/22 12:02 AM, Liu, Rong L wrote: > Hi Dmytro, > >> -----Original Message----- >> From: Dmytro Maluka <dmy@xxxxxxxxxxxx> >> Sent: Saturday, July 30, 2022 7:35 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 >> >> On 7/29/22 10:48 PM, Liu, Rong L wrote: >>> 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? >> >> Ah ok, got your point. >> >> That was my initial approach in my PoC patch posted in [1]. But then I >> dropped it, for 2 reasons: >> >> 1. Upon feedback from Sean I realized that kvm_notify_acked_irq() is >> also doing some other important things besides notifying vfio. In >> particular, in irqfd_resampler_ack() we also de-assert the vIRQ via >> kvm_set_irq(). In case of IOAPIC it means clearing its bit in IRR >> register. If we delay that until unmasking, it means that we change >> the way how KVM emulates the interrupt controller. That would seem >> inconsistent. >> > > Thanks for clarification. I totally agree that it is important to keep the way > how KVM emulates the interrupt controller. > >> Also kvm_notify_acked_irq() notifies the emulated PIT timer via >> kvm_pit_ack_irq(). I haven't analyzed how exactly that PIT stuff >> works, so I'm not sure if delaying that until unmask wouldn't cause >> any unwanted effects. >> >> So the idea is to postpone eventfd_signal() only, to fix interaction >> with vfio while keeping the rest of the KVM behavior intact. Because >> the KVM job is to emulate the interrupt controller (which it already >> does correctly), not the external device which is the job of vfio*. >> > > I made a mistake in my last post. I mean just to delay the notification of > vfio, but keep the rest of the code as intact as possible. Hmm, thanks, until now I wasn't thinking about another possibility: call delayed eventfd_signal() directly from ioapic_write_indirect(). However, now thinking about that, I don't really see advantages. We wouldn't need to use mask notifiers then, but we would still need the same logic and synchronization in irqfd_resampler_ack() for checking whether we should delay the notification. Moreover, I'm not sure how would I then address the resampler->masked initialization race issue, which I addressed in v2 by implementing kvm_register_and_fire_irq_mask_notifier() in [1]. [1] https://lore.kernel.org/lkml/20220805193919.1470653-3-dmy@xxxxxxxxxxxx/ > >> 2. kvm_notify_acked_irq() can't be called under ioapic->lock, so in [1] >> I was unlocking ioapic->lock in ioapic_write_indirect() with a naive >> assumption that it was as safe as doing it in >> kvm_ioapic_update_eoi_one(). That was probably racy, and I hadn't >> figured out how to rework it in a race-free way. >> >> [1] https://lore.kernel.org/kvm/31420943-8c5f-125c-a5ee- >> d2fde2700083@xxxxxxxxxxxx/ >> >> [*] By "vfio" I always mean "vfio or any other resamplefd user". >> >> 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 >>>>>
