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    SubjectRe: [PATCH v2 4/4] vdpa_sim: Implement stop vdpa op
    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@redhat.com>
    >---
    > 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
    >

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