KVM: arm64: gic-v5: Set up VMTEs and VPE doorbells

A GICv5 VM needs a VM table entry before it can use SPIs and LPIs,
which are backed by the host IRS. The VM table itself is created at
probe time, but each VM still needs to claim and populate one VMTE
before it can use those interrupts.

VPE doorbells are allocated from the host LPI irq domain. Without that
domain, KVM cannot issue IRS commands or receive doorbell wakeups.
Fail the GICv5 KVM probe if the host driver did not create an LPI
domain.

Allocate a VM ID during vgic_v5_init(). The VM ID is also the index
into the VM table, so allocating it selects the VMTE slot that will be
used for the lifetime of the VM.

Create a per-VM VPE doorbell irq domain, allocate one doorbell
interrupt per vCPU, request the interrupts, and keep the doorbell IRQ
number in the vCPU's GICv5 state. The doorbell handler marks the VPE
doorbell as fired, raises KVM_REQ_IRQ_PENDING, and kicks the target
vCPU so that KVM can re-evaluate pending interrupt state.

The doorbell domain indexes its interrupts using the dense vcpu_idx,
while GICv5 uses the userspace-provided vcpu_id as the VPE ID. Store a
backpointer to the VM and use it to resolve the vCPU before issuing
VPE-specific IRS commands. This preserves the userspace VPE ID when
vCPU IDs are sparse.

With the VM ID and doorbells in place, initialise the VMTE backing
state, including the VM descriptor, VPE table, and preallocated VPED
storage. The doorbells have to exist before making the VMTE valid, as
they provide the IRQ-side conduit used by the IRS commands. Make the
VMTE valid via the IRS, then populate the VPETE for each vCPU.

Add vgic_v5_teardown() to unwind the state in the reverse order. Make
the VMTE invalid, clear the per-vCPU VPETEs, release the VMTE backing
state, free the doorbell IRQs and irq domain, and finally release the
VM ID so that the VMTE slot can be reused by a later VM. If
invalidating the VMTE, clearing a VPETE, or releasing the VMTE fails,
still free the software doorbells and domain, but keep the VM ID
allocated so that the VMTE slot is not reused while hardware-visible
state may remain.

On init failure, call the same teardown path so that partially created
state is unwound consistently.

As part of resetting vCPUs, mark them as valid in the VM's VPE table.
This informs the IRS that a specific VPE may be made resident. Without
this, the IRS will treat the VPE as invalid.

Also introduce vgic_v5_send_command(), a wrapper around the VPE
doorbells. It takes a struct kvm_vcpu pointer and the command to run,
and invokes the function bound to that command through the vCPU's
doorbell.

Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Link: https://patch.msgid.link/20260904113404.4051341-15-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

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