[PATCH v2 7/7] KVM: arm64: vgic-its: Stop the VM when handling MOVALL

[Marc Zyngier]

MOVALL is a royal pain, as it requires us to iterate over all the LPIs
and move them around if they are on the correct source vcpu, and
requiring locking for each of them.

This locking can result in contention for vcpus that enter and exit
the guest, and hinders forward progress. In order to make sure such
process is not contended, just stop the VM altogether.

Nobody in their right mind uses MOVALL anyway, as this is a rather
braindead aspect of the GICv3 architecture.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/vgic/vgic-its.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index cc02d9b62bd95..094eede267e54 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -1382,6 +1382,15 @@ static int vgic_its_cmd_handle_movall(struct kvm *kvm, struct vgic_its *its,
 	if (vcpu1 == vcpu2)
 		return 0;
 
+	/*
+	 * Bulk operations such as MOVALL are a pain, as they can clash
+	 * badly locking-wise with other vcpus entering and exiting the
+	 * guest, should they be affected by it. Stopping the guest is a
+	 * safer bet to ensure uncontended access and ultimately forward
+	 * progress. Yeah...
+	 */
+	kvm_arm_halt_guest(kvm);
+
 	xa_for_each(&dist->lpi_xa, intid, irq) {
 		irq = vgic_get_irq(kvm, intid);
 		if (!irq)
@@ -1394,6 +1403,8 @@ static int vgic_its_cmd_handle_movall(struct kvm *kvm, struct vgic_its *its,
 
 	vgic_its_invalidate_cache(its);
 
+	kvm_arm_resume_guest(kvm);
+
 	return 0;
 }
 
-- 
2.47.3