Re: [PATCH v2 4/4] vdpa_sim: Implement stop vdpa op

[Stefano Garzarella]

On Tue, May 24, 2022 at 07:06:10PM +0200, Eugenio Pérez wrote:
> Implement stop operation for vdpa_sim devices, so vhost-vdpa will offer
> that backend feature and userspace can effectively stop the device.
>
> This is a must before get virtqueue indexes (base) for live migration,
> since the device could modify them after userland gets them. There are
> individual ways to perform that action for some devices
> (VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...) but there was no
> way to perform it for any vhost device (and, in particular, vhost-vdpa).
>
> After the return of ioctl with stop != 0, the device MUST finish any
> pending operations like in flight requests. It must also preserve all
> the necessary state (the virtqueue vring base plus the possible device
> specific states) that is required for restoring in the future. The
> device must not change its configuration after that point.
>
> After the return of ioctl with stop == 0, the device can continue
> processing buffers as long as typical conditions are met (vq is enabled,
> DRIVER_OK status bit is enabled, etc).
>
> In the future, we will provide features similar to
> VHOST_USER_GET_INFLIGHT_FD so the device can save pending operations.
>
> Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> ---
> drivers/vdpa/vdpa_sim/vdpa_sim.c     | 21 +++++++++++++++++++++
> drivers/vdpa/vdpa_sim/vdpa_sim.h     |  1 +
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c |  3 +++
> drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  3 +++
> 4 files changed, 28 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 50d721072beb..0515cf314bed 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -107,6 +107,7 @@ static void vdpasim_do_reset(struct vdpasim *vdpasim)
> 	for (i = 0; i < vdpasim->dev_attr.nas; i++)
> 		vhost_iotlb_reset(&vdpasim->iommu[i]);
>
> +	vdpasim->running = true;
> 	spin_unlock(&vdpasim->iommu_lock);
>
> 	vdpasim->features = 0;
> @@ -505,6 +506,24 @@ static int vdpasim_reset(struct vdpa_device *vdpa)
> 	return 0;
> }
>
> +static int vdpasim_stop(struct vdpa_device *vdpa, bool stop)
> +{
> +	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +	int i;
> +
> +	spin_lock(&vdpasim->lock);
> +	vdpasim->running = !stop;
> +	if (vdpasim->running) {
> +		/* Check for missed buffers */
> +		for (i = 0; i < vdpasim->dev_attr.nvqs; ++i)
> +			vdpasim_kick_vq(vdpa, i);
> +
> +	}
> +	spin_unlock(&vdpasim->lock);
> +
> +	return 0;
> +}
> +
> static size_t vdpasim_get_config_size(struct vdpa_device *vdpa)
> {
> 	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> @@ -694,6 +713,7 @@ static const struct vdpa_config_ops vdpasim_config_ops = {
> 	.get_status             = vdpasim_get_status,
> 	.set_status             = vdpasim_set_status,
> 	.reset			= vdpasim_reset,
> +	.stop			= vdpasim_stop,
> 	.get_config_size        = vdpasim_get_config_size,
> 	.get_config             = vdpasim_get_config,
> 	.set_config             = vdpasim_set_config,
> @@ -726,6 +746,7 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
> 	.get_status             = vdpasim_get_status,
> 	.set_status             = vdpasim_set_status,
> 	.reset			= vdpasim_reset,
> +	.stop			= vdpasim_stop,
> 	.get_config_size        = vdpasim_get_config_size,
> 	.get_config             = vdpasim_get_config,
> 	.set_config             = vdpasim_set_config,
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> index 622782e92239..061986f30911 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> @@ -66,6 +66,7 @@ struct vdpasim {
> 	u32 generation;
> 	u64 features;
> 	u32 groups;
> +	bool running;
> 	/* spinlock to synchronize iommu table */
> 	spinlock_t iommu_lock;
> };
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> index 42d401d43911..bcdb1982c378 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> @@ -204,6 +204,9 @@ static void vdpasim_blk_work(struct work_struct *work)
> 	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
> 		goto out;
>
> +	if (!vdpasim->running)
> +		goto out;
> +

Not related to this series, but I think in vdpa_sim_blk.c we should 
implement something similar to what we already do in vdpa_sim_net.c and 
re-schedule the work after X requests handled, otherwise we risk never 
stopping if there are always requests to handle.

Also for supporting multiple queues, that could be a problem, but for 
now we only support one, so there should be no problem.

I have other patches to send for vdpa_sim_blk.c, so if you want I can do 
that in my series.

Thanks,
Stefano

> 	for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
> 		struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> index 5125976a4df8..886449e88502 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> @@ -154,6 +154,9 @@ static void vdpasim_net_work(struct work_struct *work)
>
> 	spin_lock(&vdpasim->lock);
>
> +	if (!vdpasim->running)
> +		goto out;
> +
> 	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
> 		goto out;
>
> --
> 2.27.0