From: Jintack Lim <[email protected]> Currently, if a vcpu thread tries to change the active state of an interrupt which is already on the same vcpu's AP list, Since the VGIC mmio handler is called after a vcpu has already synced back the LR state to the struct vgic_irq, we can just let it proceed safely.
Signed-off-by: Jintack Lim <[email protected]> --- Changes since v1: - Reworked comment - Consider userspace accesses - Get the right requester VCPU for GICv3 private IRQ accesses - Tested using kvm-unit-tests and verified that it deadlocked without this patch and passed the test with this patch :) virt/kvm/arm/vgic/vgic-mmio.c | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c index 3654b4c..2a5db13 100644 --- a/virt/kvm/arm/vgic/vgic-mmio.c +++ b/virt/kvm/arm/vgic/vgic-mmio.c @@ -180,21 +180,37 @@ unsigned long vgic_mmio_read_active(struct kvm_vcpu *vcpu, static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq, bool new_active_state) { + struct kvm_vcpu *requester_vcpu; spin_lock(&irq->irq_lock); + + /* + * The vcpu parameter here can mean multiple things depending on how + * this function is called; when handling a trap from the kernel it + * depends on the GIC version, and these functions are also called as + * part of save/restore from userspace. + * + * Therefore, we have to figure out the requester in a reliable way. + * + * When accessing VGIC state from user space, the requester_vcpu is + * NULL, which is fine, because we guarantee that no VCPUs are running + * when accessing VGIC state from user space so irq->vcpu->cpu is + * always -1. + */ + requester_vcpu = kvm_arm_get_running_vcpu(); + /* * If this virtual IRQ was written into a list register, we * have to make sure the CPU that runs the VCPU thread has - * synced back LR state to the struct vgic_irq. We can only - * know this for sure, when either this irq is not assigned to - * anyone's AP list anymore, or the VCPU thread is not - * running on any CPUs. + * synced back the LR state to the struct vgic_irq. * - * In the opposite case, we know the VCPU thread may be on its - * way back from the guest and still has to sync back this - * IRQ, so we release and re-acquire the spin_lock to let the - * other thread sync back the IRQ. + * As long as the conditions below are true, we know the VCPU thread + * may be on its way back from the guest (we kicked the VCPU thread in + * vgic_change_active_prepare) and still has to sync back this IRQ, + * so we release and re-acquire the spin_lock to let the other thread + * sync back the IRQ. */ while (irq->vcpu && /* IRQ may have state in an LR somewhere */ + irq->vcpu != requester_vcpu && /* Current thread is not the VCPU thread */ irq->vcpu->cpu != -1) /* VCPU thread is running */ cond_resched_lock(&irq->irq_lock); -- 2.5.0 _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
