KVM: arm64: gic-v5: Implement PPI interrupt injection

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>
Link: https://patch.msgid.link/20260319154937.3619520-21-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

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