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    SubjectRe: [PATCH v2] vdpasim: support doorbell mapping
    On Mon, Dec 5, 2022 at 9:52 PM Longpeng(Mike) <longpeng2@huawei.com> wrote:
    >
    > From: Longpeng <longpeng2@huawei.com>
    >
    > Support doorbell mapping for vdpasim devices, then we can test the notify
    > passthrough feature even if there's no real hardware on hand.
    >
    > Allocates a dummy page which is used to emulate the notify page of the device,
    > all VQs share the same notify register that initiated to 0xffff. A periodic
    > work will check whether there're requests need to process ( the value of the
    > notify register is 0xffff or not ).
    >
    > This cap is disabled as default, users can enable it as follow:
    > modprobe vdpa_sim notify_passthrough=true
    >
    > Signed-off-by: Longpeng <longpeng2@huawei.com>
    > ---
    > Changes v1->v2:
    > - support both kick mode and passthrough mode. [Jason]
    > - poll the notify register first. [Jason, Michael]
    > ---
    > drivers/vdpa/vdpa_sim/vdpa_sim.c | 77 ++++++++++++++++++++++++++++++++
    > drivers/vdpa/vdpa_sim/vdpa_sim.h | 3 ++
    > 2 files changed, 80 insertions(+)
    >
    > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
    > index 7438a89ce939..07096a04dabb 100644
    > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
    > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
    > @@ -14,6 +14,7 @@
    > #include <linux/slab.h>
    > #include <linux/sched.h>
    > #include <linux/dma-map-ops.h>
    > +#include <asm/set_memory.h>
    > #include <linux/vringh.h>
    > #include <linux/vdpa.h>
    > #include <linux/vhost_iotlb.h>
    > @@ -36,9 +37,16 @@ module_param(max_iotlb_entries, int, 0444);
    > MODULE_PARM_DESC(max_iotlb_entries,
    > "Maximum number of iotlb entries for each address space. 0 means unlimited. (default: 2048)");
    >
    > +static bool notify_passthrough;
    > +module_param(notify_passthrough, bool, 0444);
    > +MODULE_PARM_DESC(notify_passthrough,
    > + "Enable vq notify(doorbell) area mapping. (default: false)");

    I'm not sure if it's worth doing this, I think we can afford the cost
    of periodic work (especially considering it's a simulator).

    > +
    > #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
    > #define VDPASIM_QUEUE_MAX 256
    > #define VDPASIM_VENDOR_ID 0
    > +#define VDPASIM_VRING_POLL_PERIOD 100 /* ms */
    > +#define VDPASIM_NOTIFY_DEFVAL 0xffff
    >
    > static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
    > {
    > @@ -246,6 +254,28 @@ static const struct dma_map_ops vdpasim_dma_ops = {
    > static const struct vdpa_config_ops vdpasim_config_ops;
    > static const struct vdpa_config_ops vdpasim_batch_config_ops;
    >
    > +static void vdpasim_notify_work(struct work_struct *work)
    > +{
    > + struct vdpasim *vdpasim;
    > + u16 *val;
    > +
    > + vdpasim = container_of(work, struct vdpasim, notify_work.work);
    > +
    > + if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
    > + goto out;
    > +
    > + if (!vdpasim->running)
    > + goto out;
    > +
    > + val = (u16 *)vdpasim->notify;
    > + if (xchg(val, VDPASIM_NOTIFY_DEFVAL) != VDPASIM_NOTIFY_DEFVAL)
    > + schedule_work(&vdpasim->work);
    > +
    > +out:
    > + schedule_delayed_work(&vdpasim->notify_work,
    > + msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
    > +}
    > +
    > struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
    > const struct vdpa_dev_set_config *config)
    > {
    > @@ -287,6 +317,18 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
    > set_dma_ops(dev, &vdpasim_dma_ops);
    > vdpasim->vdpa.mdev = dev_attr->mgmt_dev;
    >
    > + if (notify_passthrough) {
    > + INIT_DELAYED_WORK(&vdpasim->notify_work, vdpasim_notify_work);
    > +
    > + vdpasim->notify = __get_free_page(GFP_KERNEL | __GFP_ZERO);
    > + if (!vdpasim->notify)
    > + goto err_iommu;
    > +#ifdef CONFIG_X86
    > + set_memory_uc(vdpasim->notify, 1);
    > +#endif

    I had the same question with version 1, any reason for having this
    part uncacheable? It's a hint that we have bugs somewhere. Are we
    missing ACCESS/ORDER_PLATFORM or other features?

    > + *(u16 *)vdpasim->notify = VDPASIM_NOTIFY_DEFVAL;

    WRITE_ONCE()?

    > + }
    > +
    > vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
    > if (!vdpasim->config)
    > goto err_iommu;
    > @@ -495,6 +537,18 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
    > return status;
    > }
    >
    > +static void vdpasim_set_notify_work(struct vdpasim *vdpasim, bool start)
    > +{
    > + if (!notify_passthrough)
    > + return;

    Only two callers for this function: one is start another is stop. If
    we decide to get rid of notify_passthrough, I'd rather opencode the
    schedule/cancel_delayed().

    Thanks

    > +
    > + if (start)
    > + schedule_delayed_work(&vdpasim->notify_work,
    > + msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
    > + else
    > + cancel_delayed_work_sync(&vdpasim->notify_work);
    > +}
    > +
    > static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
    > {
    > struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
    > @@ -502,12 +556,14 @@ static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
    > spin_lock(&vdpasim->lock);
    > vdpasim->status = status;
    > spin_unlock(&vdpasim->lock);
    > + vdpasim_set_notify_work(vdpasim, status & VIRTIO_CONFIG_S_DRIVER_OK);
    > }
    >
    > static int vdpasim_reset(struct vdpa_device *vdpa, bool clear)
    > {
    > struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
    >
    > + vdpasim_set_notify_work(vdpasim, false);
    > spin_lock(&vdpasim->lock);
    > vdpasim->status = 0;
    > vdpasim_do_reset(vdpasim);
    > @@ -672,11 +728,24 @@ static int vdpasim_dma_unmap(struct vdpa_device *vdpa, unsigned int asid,
    > return 0;
    > }
    >
    > +static struct vdpa_notification_area
    > +vdpasim_get_vq_notification(struct vdpa_device *vdpa, u16 qid)
    > +{
    > + struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
    > + struct vdpa_notification_area notify;
    > +
    > + notify.addr = virt_to_phys((void *)vdpasim->notify);
    > + notify.size = PAGE_SIZE;
    > +
    > + return notify;
    > +}
    > +
    > static void vdpasim_free(struct vdpa_device *vdpa)
    > {
    > struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
    > int i;
    >
    > + vdpasim_set_notify_work(vdpasim, false);
    > cancel_work_sync(&vdpasim->work);
    >
    > for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
    > @@ -693,6 +762,12 @@ static void vdpasim_free(struct vdpa_device *vdpa)
    > vhost_iotlb_free(vdpasim->iommu);
    > kfree(vdpasim->vqs);
    > kfree(vdpasim->config);
    > + if (vdpasim->notify) {
    > +#ifdef CONFIG_X86
    > + set_memory_wb(vdpasim->notify, 1);
    > +#endif
    > + free_page(vdpasim->notify);
    > + }
    > }
    >
    > static const struct vdpa_config_ops vdpasim_config_ops = {
    > @@ -704,6 +779,7 @@ static const struct vdpa_config_ops vdpasim_config_ops = {
    > .get_vq_ready = vdpasim_get_vq_ready,
    > .set_vq_state = vdpasim_set_vq_state,
    > .get_vq_state = vdpasim_get_vq_state,
    > + .get_vq_notification = vdpasim_get_vq_notification,
    > .get_vq_align = vdpasim_get_vq_align,
    > .get_vq_group = vdpasim_get_vq_group,
    > .get_device_features = vdpasim_get_device_features,
    > @@ -737,6 +813,7 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
    > .get_vq_ready = vdpasim_get_vq_ready,
    > .set_vq_state = vdpasim_set_vq_state,
    > .get_vq_state = vdpasim_get_vq_state,
    > + .get_vq_notification = vdpasim_get_vq_notification,
    > .get_vq_align = vdpasim_get_vq_align,
    > .get_vq_group = vdpasim_get_vq_group,
    > .get_device_features = vdpasim_get_device_features,
    > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
    > index 0e78737dcc16..0769ccbd3911 100644
    > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
    > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
    > @@ -69,6 +69,9 @@ struct vdpasim {
    > bool running;
    > /* spinlock to synchronize iommu table */
    > spinlock_t iommu_lock;
    > + /* dummy notify page */
    > + unsigned long notify;
    > + struct delayed_work notify_work;
    > };
    >
    > struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr,
    > --
    > 2.23.0
    >

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