Re: [PATCH v5 19/36] KVM: arm64: gic-v5: Implement PPI interrupt injection

Marc Zyngier
2026-03-04T13:08:36Z

On Thu, 26 Feb 2026 16:00:21 +0000,
Sascha Bischoff <Sascha.Bischoff@arm.com> wrote:
>
> This change introduces interrupt injection for PPIs for GICv5-based
> guests.
>
> The lifecycle of PPIs is largely managed by the hardware for a GICv5
> system. The hypervisor injects pending state into the guest by using
> the ICH_PPI_PENDRx_EL2 registers. These are used by the hardware to
> pick a Highest Priority Pending Interrupt (HPPI) for the guest based
> on the enable state of each individual interrupt. The enable state and
> priority for each interrupt are provided by the guest itself (through
> writes to the PPI registers).
>
> When Direct Virtual Interrupt (DVI) is set for a particular PPI, the
> hypervisor is even able to skip the injection of the pending state
> altogether - it all happens in hardware.
>
> The result of the above is that no AP lists are required for GICv5,
> unlike for older GICs. Instead, for PPIs the ICH_PPI_* registers
> fulfil the same purpose for all 128 PPIs. Hence, as long as the
> ICH_PPI_* registers are populated prior to guest entry, and merged
> back into the KVM shadow state on exit, the PPI state is preserved,
> and interrupts can be injected.
>
> When injecting the state of a PPI the state is merged into the
> PPI-specific vgic_irq structure. The PPIs are made pending via the
> ICH_PPI_PENDRx_EL2 registers, the value of which is generated from the
> vgic_irq structures for each PPI exposed on guest entry. The
> queue_irq_unlock() irq_op is required to kick the vCPU to ensure that
> it seems the new state. The result is that no AP lists are used for
> private interrupts on GICv5.
>
> Prior to entering the guest, vgic_v5_flush_ppi_state() is called from
> kvm_vgic_flush_hwstate(). This generates the pending state to inject
> into the guest, and snapshots it (twice - an entry and an exit copy)
> in order to track any changes. These changes can come from a guest
> consuming an interrupt or from a guest making an Edge-triggered
> interrupt pending.
>
> When returning from running a guest, the guest's PPI state is merged
> back into KVM's vgic_irq state in vgic_v5_merge_ppi_state() from
> kvm_vgic_sync_hwstate(). The Enable and Active state is synced back for
> all PPIs, and the pending state is synced back for Edge PPIs (Level is
> driven directly by the devices generating said levels). The incoming
> pending state from the guest is merged with KVM's shadow state to
> avoid losing any incoming interrupts.
>
> Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> ---
> arch/arm64/kvm/vgic/vgic-v5.c | 160 ++++++++++++++++++++++++++++++++++
> arch/arm64/kvm/vgic/vgic.c | 40 +++++++--
> arch/arm64/kvm/vgic/vgic.h | 25 ++++--
> 3 files changed, 209 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/kvm/vgic/vgic-v5.c b/arch/arm64/kvm/vgic/vgic-v5.c
> index db2225aefb130..a230c45db46ee 100644
> --- a/arch/arm64/kvm/vgic/vgic-v5.c
> +++ b/arch/arm64/kvm/vgic/vgic-v5.c
> @@ -132,6 +132,166 @@ int vgic_v5_finalize_ppi_state(struct kvm *kvm)
> return 0;
> }
>
> +/*
> + * For GICv5, the PPIs are mostly directly managed by the hardware. We (the
> + * hypervisor) handle the pending, active, enable state save/restore, but don't
> + * need the PPIs to be queued on a per-VCPU AP list. Therefore, sanity check the
> + * state, unlock, and return.
> + */
> +static bool vgic_v5_ppi_queue_irq_unlock(struct kvm *kvm, struct vgic_irq *irq,
> + unsigned long flags)
> + __releases(&irq->irq_lock)
> +{
> + struct kvm_vcpu *vcpu;
> +
> + lockdep_assert_held(&irq->irq_lock);
> +
> + if (WARN_ON_ONCE(!__irq_is_ppi(KVM_DEV_TYPE_ARM_VGIC_V5, irq->intid)))
> + goto out_unlock_fail;
> +
> + vcpu = irq->target_vcpu;
> + if (WARN_ON_ONCE(!vcpu))
> + goto out_unlock_fail;
> +
> + raw_spin_unlock_irqrestore(&irq->irq_lock, flags);
> +
> + /* Directly kick the target VCPU to make sure it sees the IRQ */
> + kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> + kvm_vcpu_kick(vcpu);
> +
> + return true;
> +
> +out_unlock_fail:
> + raw_spin_unlock_irqrestore(&irq->irq_lock, flags);
> +
> + return false;
> +}
> +
> +static struct irq_ops vgic_v5_ppi_irq_ops = {
> + .queue_irq_unlock = vgic_v5_ppi_queue_irq_unlock,
> +};
> +
> +void vgic_v5_set_ppi_ops(struct vgic_irq *irq)
> +{
> + if (WARN_ON(!irq))
> + return;
> +
> + guard(raw_spinlock_irqsave)(&irq->irq_lock);
> +
> + if (!WARN_ON(irq->ops))
> + irq->ops = &vgic_v5_ppi_irq_ops;
> +}
> +
> +/*
> + * Detect any PPIs state changes, and propagate the state with KVM's
> + * shadow structures.
> + */
> +void vgic_v5_fold_ppi_state(struct kvm_vcpu *vcpu)
> +{
> + struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
> +
> + for (int reg = 0; reg < 2; reg++) {
> + const u64 activer = host_data_ptr(vgic_v5_ppi_state)->activer_exit[reg];
> + const u64 pendr = host_data_ptr(vgic_v5_ppi_state)->pendr_exit[reg];
> + unsigned long changed_bits;
> + int i;
> +
> + /*
> + * Track what changed across activer, pendr, but mask with
> + * ~DVI.
> + */
> + changed_bits = cpu_if->vgic_ppi_activer[reg] ^ activer;
> + changed_bits |= host_data_ptr(vgic_v5_ppi_state)->pendr_entry[reg] ^ pendr;
> + changed_bits &= ~cpu_if->vgic_ppi_dvir[reg];
> +
> + for_each_set_bit(i, &changed_bits, 64) {
> + struct vgic_irq *irq;
> + u32 intid;
> +
> + intid = FIELD_PREP(GICV5_HWIRQ_TYPE, GICV5_HWIRQ_TYPE_PPI);
> + intid |= FIELD_PREP(GICV5_HWIRQ_ID, reg * 64 + i);
> +
> + irq = vgic_get_vcpu_irq(vcpu, intid);
> +
> + scoped_guard(raw_spinlock_irqsave, &irq->irq_lock) {
> + irq->active = !!(activer & BIT(i));
> +
> + /*
> + * This is an OR to avoid losing incoming
> + * edges!
> + */
> + if (irq->config == VGIC_CONFIG_EDGE)
> + irq->pending_latch |= !!(pendr & BIT(i));
> + }
> +
> + vgic_put_irq(vcpu->kvm, irq);
> + }
> +
> + /*
> + * Re-inject the exit state as entry state next time!
> + *
> + * Note that the write of the Enable state is trapped, and hence
> + * there is nothing to explcitly sync back here as we already
> + * have the latest copy by definition.
> + */
> + cpu_if->vgic_ppi_activer[reg] = activer;
> + }

I think this whole thing would benefit from using bitmap operations
rather than these nested loops. I wrote the following, which isn't
very nice either (too many casts), but could be improved by either
changing the underlying types to be actual bitmaps or using
bitmap_from_arr64()...

void vgic_v5_fold_ppi_state(struct kvm_vcpu *vcpu)
{
struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
DECLARE_BITMAP(changed_pending, 128);
DECLARE_BITMAP(changed_active, 128);
DECLARE_BITMAP(changed_bits, 128);
unsigned long *activer, *pendr;
int i;

activer = (unsigned long *)&host_data_ptr(vgic_v5_ppi_state)->activer_exit;
pendr = (unsigned long *)&host_data_ptr(vgic_v5_ppi_state)->pendr_exit;

bitmap_xor(changed_active, (unsigned long *)cpu_if->vgic_ppi_activer, activer, 128);
bitmap_xor(changed_pending, (unsigned long *)host_data_ptr(vgic_v5_ppi_state)->pendr_entry, pendr, 128);
bitmap_or(changed_bits, changed_active, changed_pending, 128);

for_each_set_bit(i, changed_bits, 128) {
struct vgic_irq *irq;
bool active;
u32 intid;

intid = FIELD_PREP(GICV5_HWIRQ_TYPE, GICV5_HWIRQ_TYPE_PPI);
intid |= FIELD_PREP(GICV5_HWIRQ_ID, i);

irq = vgic_get_vcpu_irq(vcpu, intid);
active = test_bit(i, activer);

scoped_guard(raw_spinlock_irqsave, &irq->irq_lock) {
irq->active = active;

/*
* This is an OR to avoid losing incoming
* edges!
*/
if (irq->config == VGIC_CONFIG_EDGE)
irq->pending_latch |= test_bit(i, pendr);
}

/*
* Re-inject the exit state as entry state next time!
*
* Note that the write of the Enable state is trapped, and
* hence there is nothing to explcitly sync back here as we
* already have the latest copy by definition.
*/
__assign_bit(i, (unsigned long *)cpu_if->vgic_ppi_activer, active);

vgic_put_irq(vcpu->kvm, irq);
}
}

> +}
> +
> +void vgic_v5_flush_ppi_state(struct kvm_vcpu *vcpu)
> +{
> + unsigned long pendr[2];
> +
> + /*
> + * Time to enter the guest - we first need to build the guest's
> + * ICC_PPI_PENDRx_EL1, however.
> + */
> + pendr[0] = 0;
> + pendr[1] = 0;
> + for (int reg = 0; reg < 2; reg++) {
> + u64 mask = vcpu->kvm->arch.vgic.gicv5_vm.vgic_ppi_mask[reg];
> + unsigned long bm_p = 0;
> + int i;
> +
> + bitmap_from_arr64(&bm_p, &mask, 64);

Given that you are already converting a 64bit quantity, you could bite
the bullet and do all 128 bits at once.

> +
> + for_each_set_bit(i, &bm_p, 64) {
> + struct vgic_irq *irq;
> + u32 intid;
> +
> + intid = FIELD_PREP(GICV5_HWIRQ_TYPE, GICV5_HWIRQ_TYPE_PPI);
> + intid |= FIELD_PREP(GICV5_HWIRQ_ID, reg * 64 + i);
> +
> + irq = vgic_get_vcpu_irq(vcpu, intid);
> +
> + scoped_guard(raw_spinlock_irqsave, &irq->irq_lock) {
> + if (irq_is_pending(irq))
> + __assign_bit(i % 64, &pendr[reg], 1);
> + }
> +
> + vgic_put_irq(vcpu->kvm, irq);
> + }
> + }
> +
> + /*
> + * Copy the shadow state to the pending reg that will be written to the
> + * ICH_PPI_PENDRx_EL2 regs. While the guest is running we track any
> + * incoming changes to the pending state in the vgic_irq structures. The
> + * incoming changes are merged with the outgoing changes on the return
> + * path.
> + */
> + host_data_ptr(vgic_v5_ppi_state)->pendr_entry[0] = pendr[0];
> + host_data_ptr(vgic_v5_ppi_state)->pendr_entry[1] = pendr[1];
> +
> + /*
> + * Make sure that we can correctly detect "edges" in the PPI
> + * state. There's a path where we never actually enter the guest, and
> + * failure to do this risks losing pending state
> + */
> + host_data_ptr(vgic_v5_ppi_state)->pendr_exit[0] = pendr[0];
> + host_data_ptr(vgic_v5_ppi_state)->pendr_exit[1] = pendr[1];
> +}
> +
> /*
> * Sets/clears the corresponding bit in the ICH_PPI_DVIR register.
> */
> diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
> index 49d65e8cc742b..69bfa0f81624c 100644
> --- a/arch/arm64/kvm/vgic/vgic.c
> +++ b/arch/arm64/kvm/vgic/vgic.c
> @@ -105,6 +105,18 @@ struct vgic_irq *vgic_get_vcpu_irq(struct kvm_vcpu *vcpu, u32 intid)
> if (WARN_ON(!vcpu))
> return NULL;
>
> + if (vgic_is_v5(vcpu->kvm)) {
> + u32 int_num, hwirq_id;
> +
> + if (!__irq_is_ppi(KVM_DEV_TYPE_ARM_VGIC_V5, intid))
> + return NULL;
> +
> + hwirq_id = FIELD_GET(GICV5_HWIRQ_ID, intid);
> + int_num = array_index_nospec(hwirq_id, VGIC_V5_NR_PRIVATE_IRQS);
> +
> + return &vcpu->arch.vgic_cpu.private_irqs[int_num];
> + }
> +
> /* SGIs and PPIs */
> if (intid < VGIC_NR_PRIVATE_IRQS) {
> intid = array_index_nospec(intid, VGIC_NR_PRIVATE_IRQS);
> @@ -825,9 +837,11 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
> vgic_release_deleted_lpis(vcpu->kvm);
> }
>
> -static inline void vgic_fold_lr_state(struct kvm_vcpu *vcpu)
> +static void vgic_fold_state(struct kvm_vcpu *vcpu)
> {
> - if (kvm_vgic_global_state.type == VGIC_V2)
> + if (vgic_is_v5(vcpu->kvm))
> + vgic_v5_fold_ppi_state(vcpu);
> + else if (kvm_vgic_global_state.type == VGIC_V2)
> vgic_v2_fold_lr_state(vcpu);
> else
> vgic_v3_fold_lr_state(vcpu);
> @@ -1034,8 +1048,10 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> if (can_access_vgic_from_kernel())
> vgic_save_state(vcpu);
>
> - vgic_fold_lr_state(vcpu);
> - vgic_prune_ap_list(vcpu);
> + vgic_fold_state(vcpu);
> +
> + if (!vgic_is_v5(vcpu->kvm))
> + vgic_prune_ap_list(vcpu);

I'm starting to think we should have per-GIC implementations of these
things. This is becoming very tortuous.

Thanks,

M.

--
Without deviation from the norm, progress is not possible.