[PATCH 14/43] KVM: arm64: gic-v5: Request VPE doorbells when going non-resident

[Sascha Bischoff]

When a VPE is made non-resident and is entering WFI, a doorbell should
be requested for the VPE. This allows the VPE to be easily woken once
an SPI/LPI interrupt is pending for it. This is tracked by the IRS,
which will signal the specific VPE doorbell for the VPE once such an
interrupt arrives.

Requesting a doorbell involves calculating the DBPM - DoorBell
Priority Mask - which ensures that the DB is only signalled by the
hardware if the pending interrupt is of sufficient priority. This
avoids waking a VPE that can't process the incoming interrupt.

Doorbells are NOT requested if a VPE is not entering WFI as we expect
to enter again imminently.

Signed-off-by: Sascha Bischoff <sascha.bischoff at arm.com>
---
 arch/arm64/kvm/vgic/vgic-v5.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-v5.c b/arch/arm64/kvm/vgic/vgic-v5.c
index 11a1a491b7e0a..2fc6fa4df034f 100644
--- a/arch/arm64/kvm/vgic/vgic-v5.c
+++ b/arch/arm64/kvm/vgic/vgic-v5.c
@@ -1077,6 +1077,9 @@ void vgic_v5_load(struct kvm_vcpu *vcpu)
 void vgic_v5_put(struct kvm_vcpu *vcpu)
 {
 	struct vgic_v5_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v5;
+	bool req_db = !!vcpu_get_flag(vcpu, IN_WFI);
+	u32 priority_mask;
+	int dbpm;
 
 	/*
 	 * Do nothing if we're not resident. This can happen in the WFI path
@@ -1090,6 +1093,31 @@ void vgic_v5_put(struct kvm_vcpu *vcpu)
 	kvm_call_hyp(__vgic_v5_save_apr, cpu_if);
 
 	cpu_if->vgic_contextr = 0;
+	if (req_db) {
+		/*
+		 * Find the virtual running priority and use this to calculate
+		 * the doorbell priority mask. We combine the highest active
+		 * priority and the CPU's priority mask. The guest can't handle
+		 * interrupts with priorities less than or equal to the virtual
+		 * running priority, so there's literally no point in waking the
+		 * guest for these.
+		 *
+		 * The priority needs to be higher than the mask to signal, so
+		 * pick the next higher priority (subtract 1).
+		 */
+		priority_mask = vgic_v5_get_effective_priority_mask(vcpu);
+
+		/* Don't request a doorbell if the max priority is masked */
+		if (priority_mask) {
+			dbpm = priority_mask - 1;
+			cpu_if->vgic_contextr = FIELD_PREP(ICH_CONTEXTR_EL2_DB, 1) |
+						FIELD_PREP(ICH_CONTEXTR_EL2_DBPM, dbpm);
+		}
+
+		/* Make the doorbell affine to this CPU */
+		WARN_ON(irq_set_affinity(vgic_v5_vpe_db(vcpu),
+					 cpumask_of(smp_processor_id())));
+	}
 
 	kvm_call_hyp(__vgic_v5_make_non_resident, cpu_if);
 
-- 
2.34.1