KVM: arm64: gic-v5: Request doorbells when VPEs enter WFI

When a GICv5 VPE is made non-resident as part of the vcpu entering
WFI, request a VPE doorbell so that KVM can be notified when a
suitable SPI or LPI becomes pending for that VPE.

Program the doorbell priority mask, DBPM, from the effective virtual
priority mask before making the VPE non-resident. DBPM is the priority
threshold used by the GICv5 hardware to decide whether a pending SPI
or LPI is allowed to signal the VPE doorbell. This allows hardware to
signal the doorbell only for interrupts that the vcpu can actually
take, and avoids waking it for interrupts masked by the guest priority
state. If no interrupt can be signalled to the vcpu, leave the
doorbell request clear.

Attempt to make the doorbell interrupt affine to the current CPU
before requesting it. Treat affinity failures as non-fatal and
continue using the existing placement. A successful move nudges the
wakeup back towards the CPU that last ran the vcpu, where the relevant
state is more likely to be cache-hot, while also spreading doorbell
interrupts across host PEs as different vcpus enter WFI on different
CPUs.

Clear stale db_fired state before making the VPE non-resident. Any
previous doorbell notification has already been consumed by this
point, and clearing it before the non-resident transition ensures that
a newly fired doorbell is observed.

Finally, teach kvm_vgic_vcpu_pending_irq() to report pending work for
a GICv5 vcpu when its VPE doorbell has fired, in addition to the
existing pending-PPI check.

Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Link: https://patch.msgid.link/20260904113404.4051341-17-sascha.bischoff@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

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