Hi Christoffer,
thanks for submitting this patch.
On Mon, Mar 6, 2017 at 8:42 AM, Christoffer Dall
<christoffer.dall@xxxxxxxxxx> wrote:
> From: Jintack Lim <jintack@xxxxxxxxxxxxxxx>
>
> Currently, if a vcpu thread tries to change the active state of an
> interrupt which is already on the same vcpu's AP list,
"it'll loop forever" is remove accidentally in the commit message in v2?
> 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 <jintack@xxxxxxxxxxxxxxx>
> ---
> 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 :)
nice!
>
> 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
>
>
