Hi Marc,
On 14/03/18 19:37, Marc Zyngier wrote:
> It was recently reported that VFIO mediated devices, and anything
> that VFIO exposes as level interrupts, do no strictly follow the
> expected logic of such interrupts as it only lowers the input
> line when the guest has EOId the interrupt at the GIC level, rather
> than when it Acked the interrupt at the device level.
>
> THe GIC's Active+Pending state is fundamentally incompatible with
> this behaviour, as it prevents KVM from observing the EOI, and in
> turn results in VFIO never dropping the line. This results in an
> interrupt storm in the guest, which it really never expected.
>
> As we cannot really change VFIO to follow the strict rules of level
> signalling, let's forbid the A+P state altogether, as it is in the
> end only an optimization. It ensures that we will transition via
> an invalid state, which we can use to notify VFIO of the EOI.
>
> Reported-by: Shunyong Yang <shunyong.yang@xxxxxxxxxxxxxxxx>
> Tested-by: Shunyong Yang <shunyong.yang@xxxxxxxxxxxxxxxx>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
> virt/kvm/arm/vgic/vgic-v2.c | 47 +++++++++++++++++++++++++++------------------
> virt/kvm/arm/vgic/vgic-v3.c | 47 +++++++++++++++++++++++++++------------------
> 2 files changed, 56 insertions(+), 38 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
> index 29556f71b691..9356d749da1d 100644
> --- a/virt/kvm/arm/vgic/vgic-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-v2.c
> @@ -153,8 +153,35 @@ void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
> void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr)
> {
> u32 val = irq->intid;
> + bool allow_pending = true;
>
> - if (irq_is_pending(irq)) {
> + if (irq->active)
> + val |= GICH_LR_ACTIVE_BIT;
> +
> + if (irq->hw) {
> + val |= GICH_LR_HW;
> + val |= irq->hwintid << GICH_LR_PHYSID_CPUID_SHIFT;
> + /*
> + * Never set pending+active on a HW interrupt, as the
> + * pending state is kept at the physical distributor
> + * level.
> + */
> + if (irq->active)
> + allow_pending = false;
> + } else {
> + if (irq->config == VGIC_CONFIG_LEVEL) {
> + val |= GICH_LR_EOI;
> +
> + /*
> + * Software resampling doesn't work very well
> + * if we allow P+A, so let's not do that.
> + */
> + if (irq->active)
> + allow_pending = false;
> + }
> + }
> +
> + if (allow_pending && irq_is_pending(irq)) {
> val |= GICH_LR_PENDING_BIT;
Can't we have this no luck unlikely scenario where soft_pending and LR
state A on flush? In such case, on fold we are going to reset the
pending_latch as we considered disappearance of LR P meant the
soft_pending was acked. But P now is no more logged in LR concurrently
with A.
Thanks
Eric
>
> if (irq->config == VGIC_CONFIG_EDGE)
> @@ -171,24 +198,6 @@ void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr)
> }
> }
>
> - if (irq->active)
> - val |= GICH_LR_ACTIVE_BIT;
> -
> - if (irq->hw) {
> - val |= GICH_LR_HW;
> - val |= irq->hwintid << GICH_LR_PHYSID_CPUID_SHIFT;
> - /*
> - * Never set pending+active on a HW interrupt, as the
> - * pending state is kept at the physical distributor
> - * level.
> - */
> - if (irq->active && irq_is_pending(irq))
> - val &= ~GICH_LR_PENDING_BIT;
> - } else {
> - if (irq->config == VGIC_CONFIG_LEVEL)
> - 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
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index 0ff2006f3781..6b484575cafb 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -135,8 +135,35 @@ void vgic_v3_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr)
> {
> u32 model = vcpu->kvm->arch.vgic.vgic_model;
> u64 val = irq->intid;
> + bool allow_pending = true;
>
> - if (irq_is_pending(irq)) {
> + if (irq->active)
> + val |= ICH_LR_ACTIVE_BIT;
> +
> + if (irq->hw) {
> + val |= ICH_LR_HW;
> + val |= ((u64)irq->hwintid) << ICH_LR_PHYS_ID_SHIFT;
> + /*
> + * Never set pending+active on a HW interrupt, as the
> + * pending state is kept at the physical distributor
> + * level.
> + */
> + if (irq->active)
> + allow_pending = false;
> + } else {
> + if (irq->config == VGIC_CONFIG_LEVEL) {
> + val |= ICH_LR_EOI;
> +
> + /*
> + * Software resampling doesn't work very well
> + * if we allow P+A, so let's not do that.
> + */
> + if (irq->active)
> + allow_pending = false;
> + }
> + }
> +
> + if (allow_pending && irq_is_pending(irq)) {
> val |= ICH_LR_PENDING_BIT;
>
> if (irq->config == VGIC_CONFIG_EDGE)
> @@ -154,24 +181,6 @@ void vgic_v3_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr)
> }
> }
>
> - if (irq->active)
> - val |= ICH_LR_ACTIVE_BIT;
> -
> - if (irq->hw) {
> - val |= ICH_LR_HW;
> - val |= ((u64)irq->hwintid) << ICH_LR_PHYS_ID_SHIFT;
> - /*
> - * Never set pending+active on a HW interrupt, as the
> - * pending state is kept at the physical distributor
> - * level.
> - */
> - if (irq->active && irq_is_pending(irq))
> - val &= ~ICH_LR_PENDING_BIT;
> - } else {
> - if (irq->config == VGIC_CONFIG_LEVEL)
> - 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
>
