Re: [PATCH v8 06/17] KVM: arm/arm64: VGIC: add refcounting for IRQs

Christoffer Dall
2016-07-07T13:13:57Z

On Tue, Jul 05, 2016 at 12:22:58PM +0100, Andre Przywara wrote:
> In the moment our struct vgic_irq's are statically allocated at guest
> creation time. So getting a pointer to an IRQ structure is trivial and
> safe. LPIs are more dynamic, they can be mapped and unmapped at any time
> during the guest's _runtime_.
> In preparation for supporting LPIs we introduce reference counting for
> those structures using the kernel's kref infrastructure.
> Since private IRQs and SPIs are statically allocated, the refcount never
> drops to 0 at the moment, but we increase it when an IRQ gets onto a VCPU
> list and decrease it when it gets removed.
> This introduces vgic_put_irq(), which wraps kref_put and hides the
> release function from the callers.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> include/kvm/arm_vgic.h | 1 +
> virt/kvm/arm/vgic/vgic-init.c | 2 ++
> virt/kvm/arm/vgic/vgic-mmio-v2.c | 8 +++++++
> virt/kvm/arm/vgic/vgic-mmio-v3.c | 20 +++++++++++------
> virt/kvm/arm/vgic/vgic-mmio.c | 25 ++++++++++++++++++++-
> virt/kvm/arm/vgic/vgic-v2.c | 1 +
> virt/kvm/arm/vgic/vgic-v3.c | 1 +
> virt/kvm/arm/vgic/vgic.c | 48 +++++++++++++++++++++++++++++++---------
> virt/kvm/arm/vgic/vgic.h | 1 +
> 9 files changed, 89 insertions(+), 18 deletions(-)
>
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 5142e2a..450b4da 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -96,6 +96,7 @@ struct vgic_irq {
> bool active; /* not used for LPIs */
> bool enabled;
> bool hw; /* Tied to HW IRQ */
> + struct kref refcount; /* Used for LPIs */
> u32 hwintid; /* HW INTID number */
> union {
> u8 targets; /* GICv2 target VCPUs mask */
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index 90cae48..ac3c1a5 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -177,6 +177,7 @@ static int kvm_vgic_dist_init(struct kvm *kvm, unsigned int nr_spis)
> spin_lock_init(&irq->irq_lock);
> irq->vcpu = NULL;
> irq->target_vcpu = vcpu0;
> + kref_init(&irq->refcount);
> if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V2)
> irq->targets = 0;
> else
> @@ -211,6 +212,7 @@ static void kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
> irq->vcpu = NULL;
> irq->target_vcpu = vcpu;
> irq->targets = 1U << vcpu->vcpu_id;
> + kref_init(&irq->refcount);
> if (vgic_irq_is_sgi(i)) {
> /* SGIs */
> irq->enabled = 1;
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-mmio-v2.c
> index a213936..4152348 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
> @@ -102,6 +102,7 @@ static void vgic_mmio_write_sgir(struct kvm_vcpu *source_vcpu,
> irq->source |= 1U << source_vcpu->vcpu_id;
>
> vgic_queue_irq_unlock(source_vcpu->kvm, irq);
> + vgic_put_irq(source_vcpu->kvm, irq);
> }
> }
>
> @@ -116,6 +117,8 @@ static unsigned long vgic_mmio_read_target(struct kvm_vcpu *vcpu,
> struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
>
> val |= (u64)irq->targets << (i * 8);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> return val;
> @@ -143,6 +146,7 @@ static void vgic_mmio_write_target(struct kvm_vcpu *vcpu,
> irq->target_vcpu = kvm_get_vcpu(vcpu->kvm, target);
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -157,6 +161,8 @@ static unsigned long vgic_mmio_read_sgipend(struct kvm_vcpu *vcpu,
> struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
>
> val |= (u64)irq->source << (i * 8);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
> return val;
> }
> @@ -178,6 +184,7 @@ static void vgic_mmio_write_sgipendc(struct kvm_vcpu *vcpu,
> irq->pending = false;
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -201,6 +208,7 @@ static void vgic_mmio_write_sgipends(struct kvm_vcpu *vcpu,
> } else {
> spin_unlock(&irq->irq_lock);
> }
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> index fc7b6c9..bfcafbd 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> @@ -80,15 +80,17 @@ static unsigned long vgic_mmio_read_irouter(struct kvm_vcpu *vcpu,
> {
> int intid = VGIC_ADDR_TO_INTID(addr, 64);
> struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, NULL, intid);
> + unsigned long ret = 0;
>
> if (!irq)
> return 0;
>
> /* The upper word is RAZ for us. */
> - if (addr & 4)
> - return 0;
> + if (!(addr & 4))
> + ret = extract_bytes(READ_ONCE(irq->mpidr), addr & 7, len);
>
> - return extract_bytes(READ_ONCE(irq->mpidr), addr & 7, len);
> + vgic_put_irq(vcpu->kvm, irq);
> + return ret;
> }
>
> static void vgic_mmio_write_irouter(struct kvm_vcpu *vcpu,
> @@ -96,15 +98,17 @@ static void vgic_mmio_write_irouter(struct kvm_vcpu *vcpu,
> unsigned long val)
> {
> int intid = VGIC_ADDR_TO_INTID(addr, 64);
> - struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, NULL, intid);
> -
> - if (!irq)
> - return;
> + struct vgic_irq *irq;
>
> /* The upper word is WI for us since we don't implement Aff3. */
> if (addr & 4)
> return;
>
> + irq = vgic_get_irq(vcpu->kvm, NULL, intid);
> +
> + if (!irq)
> + return;
> +
> spin_lock(&irq->irq_lock);
>
> /* We only care about and preserve Aff0, Aff1 and Aff2. */
> @@ -112,6 +116,7 @@ static void vgic_mmio_write_irouter(struct kvm_vcpu *vcpu,
> irq->target_vcpu = kvm_mpidr_to_vcpu(vcpu->kvm, irq->mpidr);
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> static unsigned long vgic_mmio_read_v3r_typer(struct kvm_vcpu *vcpu,
> @@ -445,5 +450,6 @@ void vgic_v3_dispatch_sgi(struct kvm_vcpu *vcpu, u64 reg)
> irq->pending = true;
>
> vgic_queue_irq_unlock(vcpu->kvm, irq);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
> diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c
> index 9f6fab7..5e79e01 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio.c
> @@ -56,6 +56,8 @@ unsigned long vgic_mmio_read_enable(struct kvm_vcpu *vcpu,
>
> if (irq->enabled)
> value |= (1U << i);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> return value;
> @@ -74,6 +76,8 @@ void vgic_mmio_write_senable(struct kvm_vcpu *vcpu,
> spin_lock(&irq->irq_lock);
> irq->enabled = true;
> vgic_queue_irq_unlock(vcpu->kvm, irq);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -92,6 +96,7 @@ void vgic_mmio_write_cenable(struct kvm_vcpu *vcpu,
> irq->enabled = false;
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -108,6 +113,8 @@ unsigned long vgic_mmio_read_pending(struct kvm_vcpu *vcpu,
>
> if (irq->pending)
> value |= (1U << i);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> return value;
> @@ -129,6 +136,7 @@ void vgic_mmio_write_spending(struct kvm_vcpu *vcpu,
> irq->soft_pending = true;
>
> vgic_queue_irq_unlock(vcpu->kvm, irq);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -152,6 +160,7 @@ void vgic_mmio_write_cpending(struct kvm_vcpu *vcpu,
> }
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -168,6 +177,8 @@ unsigned long vgic_mmio_read_active(struct kvm_vcpu *vcpu,
>
> if (irq->active)
> value |= (1U << i);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> return value;
> @@ -242,6 +253,7 @@ void vgic_mmio_write_cactive(struct kvm_vcpu *vcpu,
> for_each_set_bit(i, &val, len * 8) {
> struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
> vgic_mmio_change_active(vcpu, irq, false);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> vgic_change_active_finish(vcpu, intid);
> }
> @@ -257,6 +269,7 @@ void vgic_mmio_write_sactive(struct kvm_vcpu *vcpu,
> for_each_set_bit(i, &val, len * 8) {
> struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
> vgic_mmio_change_active(vcpu, irq, true);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> vgic_change_active_finish(vcpu, intid);
> }
> @@ -272,6 +285,8 @@ unsigned long vgic_mmio_read_priority(struct kvm_vcpu *vcpu,
> struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
>
> val |= (u64)irq->priority << (i * 8);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> return val;
> @@ -298,6 +313,8 @@ void vgic_mmio_write_priority(struct kvm_vcpu *vcpu,
> /* Narrow the priority range to what we actually support */
> irq->priority = (val >> (i * 8)) & GENMASK(7, 8 - VGIC_PRI_BITS);
> spin_unlock(&irq->irq_lock);
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> @@ -313,6 +330,8 @@ unsigned long vgic_mmio_read_config(struct kvm_vcpu *vcpu,
>
> if (irq->config == VGIC_CONFIG_EDGE)
> value |= (2U << (i * 2));
> +
> + vgic_put_irq(vcpu->kvm, irq);
> }
>
> return value;
> @@ -326,7 +345,7 @@ void vgic_mmio_write_config(struct kvm_vcpu *vcpu,
> int i;
>
> for (i = 0; i < len * 4; i++) {
> - struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
> + struct vgic_irq *irq;
>
> /*
> * The configuration cannot be changed for SGIs in general,
> @@ -337,14 +356,18 @@ void vgic_mmio_write_config(struct kvm_vcpu *vcpu,
> if (intid + i < VGIC_NR_PRIVATE_IRQS)
> continue;
>
> + irq = vgic_get_irq(vcpu->kvm, vcpu, intid + i);
> spin_lock(&irq->irq_lock);
> +
> if (test_bit(i * 2 + 1, &val)) {
> irq->config = VGIC_CONFIG_EDGE;
> } else {
> irq->config = VGIC_CONFIG_LEVEL;
> irq->pending = irq->line_level | irq->soft_pending;
> }
> +
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
> index 079bf67..0bf6709 100644
> --- a/virt/kvm/arm/vgic/vgic-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-v2.c
> @@ -124,6 +124,7 @@ void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
> }
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index e48a22e..f0ac064 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -113,6 +113,7 @@ void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
> }
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> }
> }
>
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 69b61ab..ae80894 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -48,13 +48,20 @@ struct vgic_global __section(.hyp.text) kvm_vgic_global_state;
> struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
> u32 intid)
> {
> - /* SGIs and PPIs */
> - if (intid <= VGIC_MAX_PRIVATE)
> - return &vcpu->arch.vgic_cpu.private_irqs[intid];
> + struct vgic_dist *dist = &kvm->arch.vgic;
> + struct vgic_irq *irq;
>
> - /* SPIs */
> - if (intid <= VGIC_MAX_SPI)
> - return &kvm->arch.vgic.spis[intid - VGIC_NR_PRIVATE_IRQS];
> + if (intid <= VGIC_MAX_PRIVATE) { /* SGIs and PPIs */
> + irq = &vcpu->arch.vgic_cpu.private_irqs[intid];
> + kref_get(&irq->refcount);
> + return irq;
> + }
> +
> + if (intid <= VGIC_MAX_SPI) { /* SPIs */
> + irq = &dist->spis[intid - VGIC_NR_PRIVATE_IRQS];
> + kref_get(&irq->refcount);
> + return irq;
> + }

It appears to me that this could be made nicer (the diff as well) by
just setting the IRQ variable and at the end of the function do:

if (irq)
kref_get(irq->refcount);
return irq;

Perhaps a later patch will do something like that or make it obvious why
that's not a good idea.

Again, not a reason for a respin on its own.

>
> /* LPIs are not yet covered */
> if (intid >= VGIC_MIN_LPI)
> @@ -64,6 +71,17 @@ struct vgic_irq *vgic_get_irq(struct kvm *kvm, struct kvm_vcpu *vcpu,
> return NULL;
> }
>
> +/* The refcount should never drop to 0 at the moment. */
> +static void vgic_irq_release(struct kref *ref)
> +{
> + WARN_ON(1);
> +}
> +
> +void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
> +{
> + kref_put(&irq->refcount, vgic_irq_release);
> +}
> +
> /**
> * kvm_vgic_target_oracle - compute the target vcpu for an irq
> *
> @@ -236,6 +254,7 @@ retry:
> goto retry;
> }
>
> + kref_get(&irq->refcount);
> list_add_tail(&irq->ap_list, &vcpu->arch.vgic_cpu.ap_list_head);
> irq->vcpu = vcpu;
>
> @@ -269,14 +288,17 @@ static int vgic_update_irq_pending(struct kvm *kvm, int cpuid,
> if (!irq)
> return -EINVAL;
>
> - if (irq->hw != mapped_irq)
> + if (irq->hw != mapped_irq) {
> + vgic_put_irq(kvm, irq);
> return -EINVAL;
> + }
>
> spin_lock(&irq->irq_lock);
>
> if (!vgic_validate_injection(irq, level)) {
> /* Nothing to see here, move along... */
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(kvm, irq);
> return 0;
> }
>
> @@ -288,6 +310,7 @@ static int vgic_update_irq_pending(struct kvm *kvm, int cpuid,
> }
>
> vgic_queue_irq_unlock(kvm, irq);
> + vgic_put_irq(kvm, irq);
>
> return 0;
> }
> @@ -330,25 +353,28 @@ int kvm_vgic_map_phys_irq(struct kvm_vcpu *vcpu, u32 virt_irq, u32 phys_irq)
> irq->hwintid = phys_irq;
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
>
> return 0;
> }
>
> int kvm_vgic_unmap_phys_irq(struct kvm_vcpu *vcpu, unsigned int virt_irq)
> {
> - struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, virt_irq);
> -
> - BUG_ON(!irq);
> + struct vgic_irq *irq;
>
> if (!vgic_initialized(vcpu->kvm))
> return -EAGAIN;
>
> + irq = vgic_get_irq(vcpu->kvm, vcpu, virt_irq);
> + BUG_ON(!irq);
> +
> spin_lock(&irq->irq_lock);
>
> irq->hw = false;
> irq->hwintid = 0;
>
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
>
> return 0;
> }
> @@ -386,6 +412,7 @@ retry:
> list_del(&irq->ap_list);
> irq->vcpu = NULL;
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
> continue;
> }
>
> @@ -614,6 +641,7 @@ bool kvm_vgic_map_is_active(struct kvm_vcpu *vcpu, unsigned int virt_irq)
> spin_lock(&irq->irq_lock);
> map_is_active = irq->hw && irq->active;
> spin_unlock(&irq->irq_lock);
> + vgic_put_irq(vcpu->kvm, irq);
>
> return map_is_active;
> }
> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
> index c752152..5b79c34 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -38,6 +38,7 @@ struct vgic_vmcr {
>
> 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_queue_irq_unlock(struct kvm *kvm, struct vgic_irq *irq);
> void vgic_kick_vcpus(struct kvm *kvm);
>
> --
> 2.9.0
>

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>