Hi Christoffer, On 07/12/17 11:54, Christoffer Dall wrote: > Level-triggered mapped IRQs are special because we only observe rising > edges as input to the VGIC, and we don't set the EOI flag and therefore > are not told when the level goes down, so that we can re-queue a new > interrupt when the level goes up. > > One way to solve this problem is to side-step the logic of the VGIC and > special case the validation in the injection path, but it has the > unfortunate drawback of having to peak into the physical GIC state > whenever we want to know if the interrupt is pending on the virtual > distributor. > > Instead, we can maintain the current semantics of a level triggered > interrupt by sort of treating it as an edge-triggered interrupt, > following from the fact that we only observe an asserting edge. This > requires us to be a bit careful when populating the LRs and when folding > the state back in though: > > * We lower the line level when populating the LR, so that when > subsequently observing an asserting edge, the VGIC will do the right > thing. > > * If the guest never acked the interrupt while running (for example if > it had masked interrupts at the CPU level while running), we have > to preserve the pending state of the LR and move it back to the > line_level field of the struct irq when folding LR state. > > If the guest never acked the interrupt while running, but changed the > device state and lowered the line (again with interrupts masked) then > we need to observe this change in the line_level. > > Both of the above situations are solved by sampling the physical line > and set the line level when folding the LR back. > > * Finally, if the guest never acked the interrupt while running and > sampling the line reveals that the device state has changed and the > line has been lowered, we must clear the physical active state, since > we will otherwise never be told when the interrupt becomes asserted > again. > > This has the added benefit of making the timer optimization patches > (https://lists.cs.columbia.edu/pipermail/kvmarm/2017-July/026343.html) a > bit simpler, because the timer code doesn't have to clear the active > state on the sync anymore. It also potentially improves the performance > of the timer implementation because the GIC knows the state or the LR > and only needs to clear the > active state when the pending bit in the LR is still set, where the > timer has to always clear it when returning from running the guest with > an injected timer interrupt. > > Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx> > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> Looks good to me. Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx> Thanks Eric > --- > virt/kvm/arm/vgic/vgic-v2.c | 29 +++++++++++++++++++++++++++++ > virt/kvm/arm/vgic/vgic-v3.c | 29 +++++++++++++++++++++++++++++ > virt/kvm/arm/vgic/vgic.c | 23 +++++++++++++++++++++++ > virt/kvm/arm/vgic/vgic.h | 7 +++++++ > 4 files changed, 88 insertions(+) > > diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c > index 80897102da26..c32d7b93ffd1 100644 > --- a/virt/kvm/arm/vgic/vgic-v2.c > +++ b/virt/kvm/arm/vgic/vgic-v2.c > @@ -105,6 +105,26 @@ void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu) > irq->pending_latch = false; > } > > + /* > + * Level-triggered mapped IRQs are special because we only > + * observe rising edges as input to the VGIC. > + * > + * If the guest never acked the interrupt we have to sample > + * the physical line and set the line level, because the > + * device state could have changed or we simply need to > + * process the still pending interrupt later. > + * > + * If this causes us to lower the level, we have to also clear > + * the physical active state, since we will otherwise never be > + * told when the interrupt becomes asserted again. > + */ > + if (vgic_irq_is_mapped_level(irq) && (val & GICH_LR_PENDING_BIT)) { > + irq->line_level = vgic_get_phys_line_level(irq); > + > + if (!irq->line_level) > + vgic_irq_set_phys_active(irq, false); > + } > + > spin_unlock_irqrestore(&irq->irq_lock, flags); > vgic_put_irq(vcpu->kvm, irq); > } > @@ -162,6 +182,15 @@ void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr) > val |= GICH_LR_EOI; > } > > + /* > + * Level-triggered mapped IRQs are special because we only observe > + * rising edges as input to the VGIC. We therefore lower the line > + * level here, so that we can take new virtual IRQs. See > + * vgic_v2_fold_lr_state for more info. > + */ > + if (vgic_irq_is_mapped_level(irq) && (val & GICH_LR_PENDING_BIT)) > + irq->line_level = false; > + > /* The GICv2 LR only holds five bits of priority. */ > val |= (irq->priority >> 3) << GICH_LR_PRIORITY_SHIFT; > > diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c > index 2f05f732d3fd..a14423a0d383 100644 > --- a/virt/kvm/arm/vgic/vgic-v3.c > +++ b/virt/kvm/arm/vgic/vgic-v3.c > @@ -96,6 +96,26 @@ void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu) > irq->pending_latch = false; > } > > + /* > + * Level-triggered mapped IRQs are special because we only > + * observe rising edges as input to the VGIC. > + * > + * If the guest never acked the interrupt we have to sample > + * the physical line and set the line level, because the > + * device state could have changed or we simply need to > + * process the still pending interrupt later. > + * > + * If this causes us to lower the level, we have to also clear > + * the physical active state, since we will otherwise never be > + * told when the interrupt becomes asserted again. > + */ > + if (vgic_irq_is_mapped_level(irq) && (val & ICH_LR_PENDING_BIT)) { > + irq->line_level = vgic_get_phys_line_level(irq); > + > + if (!irq->line_level) > + vgic_irq_set_phys_active(irq, false); > + } > + > spin_unlock_irqrestore(&irq->irq_lock, flags); > vgic_put_irq(vcpu->kvm, irq); > } > @@ -145,6 +165,15 @@ void vgic_v3_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr) > val |= ICH_LR_EOI; > } > > + /* > + * Level-triggered mapped IRQs are special because we only observe > + * rising edges as input to the VGIC. We therefore lower the line > + * level here, so that we can take new virtual IRQs. See > + * vgic_v3_fold_lr_state for more info. > + */ > + if (vgic_irq_is_mapped_level(irq) && (val & ICH_LR_PENDING_BIT)) > + irq->line_level = false; > + > /* > * We currently only support Group1 interrupts, which is a > * known defect. This needs to be addressed at some point. > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c > index b168a328a9e0..607cbbc27a1c 100644 > --- a/virt/kvm/arm/vgic/vgic.c > +++ b/virt/kvm/arm/vgic/vgic.c > @@ -144,6 +144,29 @@ void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq) > kfree(irq); > } > > +/* Get the input level of a mapped IRQ directly from the physical GIC */ > +bool vgic_get_phys_line_level(struct vgic_irq *irq) > +{ > + bool line_level; > + > + BUG_ON(!irq->hw); > + > + WARN_ON(irq_get_irqchip_state(irq->host_irq, > + IRQCHIP_STATE_PENDING, > + &line_level)); > + return line_level; > +} > + > +/* Set/Clear the physical active state */ > +void vgic_irq_set_phys_active(struct vgic_irq *irq, bool active) > +{ > + > + BUG_ON(!irq->hw); > + WARN_ON(irq_set_irqchip_state(irq->host_irq, > + IRQCHIP_STATE_ACTIVE, > + active)); > +} > + > /** > * kvm_vgic_target_oracle - compute the target vcpu for an irq > * > diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h > index efbcf8f96f9c..d0787983a357 100644 > --- a/virt/kvm/arm/vgic/vgic.h > +++ b/virt/kvm/arm/vgic/vgic.h > @@ -104,6 +104,11 @@ static inline bool irq_is_pending(struct vgic_irq *irq) > return irq->pending_latch || irq->line_level; > } > > +static inline bool vgic_irq_is_mapped_level(struct vgic_irq *irq) > +{ > + return irq->config == VGIC_CONFIG_LEVEL && irq->hw; > +} > + > /* > * This struct provides an intermediate representation of the fields contained > * in the GICH_VMCR and ICH_VMCR registers, such that code exporting the GIC > @@ -140,6 +145,8 @@ vgic_get_mmio_region(struct kvm_vcpu *vcpu, struct vgic_io_device *iodev, > struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu, > u32 intid); > void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq); > +bool vgic_get_phys_line_level(struct vgic_irq *irq); > +void vgic_irq_set_phys_active(struct vgic_irq *irq, bool active); > bool vgic_queue_irq_unlock(struct kvm *kvm, struct vgic_irq *irq, > unsigned long flags); > void vgic_kick_vcpus(struct kvm *kvm); >
