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Date:   Mon, 28 Nov 2022 07:20:20 -0500
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>
Cc:     Jason Wang <jasowang@redhat.com>, stefanha@redhat.com,
        sgarzare@redhat.com, eperezma@redhat.com, cohuck@redhat.com,
        arei.gonglei@huawei.com, yechuan@huawei.com,
        huangzhichao@huawei.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vdpasim: support doorbell mapping
Message-ID: <20221128071917-mutt-send-email-mst@kernel.org>
References: <20221128025558.2152-1-longpeng2@huawei.com>
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 <53edc14a-74bb-f9c7-06bd-7ea1047fe613@huawei.com>
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 <28c1ae52-38ff-42ce-4331-11f7aa040296@huawei.com>
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On Mon, Nov 28, 2022 at 07:59:33PM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
> 
> 
> 在 2022/11/28 18:19, Michael S. Tsirkin 写道:
> > On Mon, Nov 28, 2022 at 04:19:30PM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
> > > 
> > > 
> > > 在 2022/11/28 12:05, Jason Wang 写道:
> > > > On Mon, Nov 28, 2022 at 10:56 AM 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.
> > > > 
> > > > You can use vp_vdpa in L1 plus page_ver_vq in L0 to test it in L2.
> > > > That is how I test it.
> > > > 
> > > Yes, using nested virtualization can work, but it's hard to deploy in my
> > > working environment for some reasons, so I decided to emulate this
> > > capability in vdpasim, it's much easier.
> > > 
> > > > > 
> > > > > Allocates a dummy page which used to emulate the notify page of the device.
> > > > > All values written to this page would be ignored,  a periodic work will
> > > > > check whether there're requests that need to process.
> > > > 
> > > > This seems tricky, it means the device is working even if there's no
> > > 
> > > Right. It just try to make the vdpasim device work properly, but the vdpasim
> > > device is only used for testing, so maybe the tricky emulation is
> > > acceptable?
> > 
> > Maybe. You can try enabling VIRTIO_F_NOTIFICATION_DATA and then
> > looking at the data written to figure out whether
> > you need to poll the vq.
> > 
> We can try after the kernel supports the VIRTIO_F_NOTIFICATION_DATA feature,
> while there is still a long way to go.

That would be up to you to implement ;) It's probably 10-20 lines of
code all in all.

> > 
> > > > kick. If we really want to do, we should try to use page fault handler
> > > > (probably by extending the config ops), but I'm not sure it's worth to
> > > > bother (or if we can find a use case for no simulator devices).
> > > > 
> > > This need to modify the framework, it seems unworthy.
> > > 
> > > > > 
> > > > > 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>
> > > > > ---
> > > > >    drivers/vdpa/vdpa_sim/vdpa_sim.c     | 71 ++++++++++++++++++++++++++--
> > > > >    drivers/vdpa/vdpa_sim/vdpa_sim.h     |  5 +-
> > > > >    drivers/vdpa/vdpa_sim/vdpa_sim_blk.c |  5 +-
> > > > >    drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  4 +-
> > > > >    4 files changed, 76 insertions(+), 9 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> > > > > index 7438a89ce939..5c215b56b78b 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 +37,15 @@ 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)");
> > > > > +
> > > > >    #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
> > > > >    #define VDPASIM_QUEUE_MAX 256
> > > > >    #define VDPASIM_VENDOR_ID 0
> > > > > +#define VDPASIM_VRING_POLL_PERIOD 100 /* ms */
> > > > > 
> > > > >    static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
> > > > >    {
> > > > > @@ -276,7 +283,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
> > > > >           }
> > > > > 
> > > > >           vdpasim->dev_attr = *dev_attr;
> > > > > -       INIT_WORK(&vdpasim->work, dev_attr->work_fn);
> > > > > +       INIT_DELAYED_WORK(&vdpasim->vring_work, dev_attr->work_fn);
> > > > >           spin_lock_init(&vdpasim->lock);
> > > > >           spin_lock_init(&vdpasim->iommu_lock);
> > > > > 
> > > > > @@ -287,6 +294,15 @@ 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) {
> > > > > +               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
> > > > 
> > > > What's the reason for using uc memory?
> > > > 
> > > The vma->vm_page_prot of notify mapping is pgprot_noncached (see
> > > vhost_vdpa_fault) but the vdpasim->notify is WB, so we should set its
> > > memtype to UC here and set it back to WB when releasing the device.
> > 
> > You never look at this memory though. Why does it matter whether
> > it's UC or WB?
> > 
> 
> The warning in trace_pfn_remap() would be triggered.
> 
> For example:
> 
> x86/PAT: CPU 16/KVM:17819 map pfn RAM range req uncached-minus for [mem
> 0x5151f3000-0x5151f3fff], got write-back
> 
> 
> > > > > +       }
> > > > > +
> > > > >           vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
> > > > >           if (!vdpasim->config)
> > > > >                   goto err_iommu;
> > > > > @@ -357,8 +373,11 @@ static void vdpasim_kick_vq(struct vdpa_device *vdpa, u16 idx)
> > > > >           struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> > > > >           struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
> > > > > 
> > > > > +       if (notify_passthrough)
> > > > > +               return;
> > > > 
> > > > So we should keep the two paths to be used at the same time. Userspace
> > > > can choose to not map doorbells?
> > > > 
> > > It can work even if the userspace does not to map doorbells (e.g start
> > > without page-per-vq=on), because the device will periodic check its vqs.
> > > 
> > > > Thanks
> > > > 
> > > > > +
> > > > >           if (vq->ready)
> > > > > -               schedule_work(&vdpasim->work);
> > > > > +               schedule_work(&vdpasim->vring_work.work);
> > > > >    }
> > > > > 
> > > > >    static void vdpasim_set_vq_cb(struct vdpa_device *vdpa, u16 idx,
> > > > > @@ -495,6 +514,18 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
> > > > >           return status;
> > > > >    }
> > > > > 
> > > > > +static void vdpasim_set_vring_work(struct vdpasim *vdpasim, bool start)
> > > > > +{
> > > > > +       if (!notify_passthrough)
> > > > > +               return;
> > > > > +
> > > > > +       if (start)
> > > > > +               schedule_delayed_work(&vdpasim->vring_work,
> > > > > +                               msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
> > > > > +       else
> > > > > +               cancel_delayed_work_sync(&vdpasim->vring_work);
> > > > > +}
> > > > > +
> > > > >    static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
> > > > >    {
> > > > >           struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> > > > > @@ -502,12 +533,16 @@ static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
> > > > >           spin_lock(&vdpasim->lock);
> > > > >           vdpasim->status = status;
> > > > >           spin_unlock(&vdpasim->lock);
> > > > > +
> > > > > +       vdpasim_set_vring_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_vring_work(vdpasim, false);
> > > > > +
> > > > >           spin_lock(&vdpasim->lock);
> > > > >           vdpasim->status = 0;
> > > > >           vdpasim_do_reset(vdpasim);
> > > > > @@ -672,12 +707,24 @@ 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;
> > > > > 
> > > > > -       cancel_work_sync(&vdpasim->work);
> > > > > +       cancel_delayed_work_sync(&vdpasim->vring_work);
> > > > > 
> > > > >           for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
> > > > >                   vringh_kiov_cleanup(&vdpasim->vqs[i].out_iov);
> > > > > @@ -693,7 +740,23 @@ 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);
> > > > > +       }
> > > > > +}
> > > > > +
> > > > > +void vdpasim_schedule_work(struct vdpasim *vdpasim, bool sched_now)
> > > > > +{
> > > > > +       if (sched_now)
> > > > > +               schedule_work(&vdpasim->vring_work.work);
> > > > > +       else if (notify_passthrough)
> > > > > +               schedule_delayed_work(&vdpasim->vring_work,
> > > > > +                                     msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
> > > > >    }
> > > > > +EXPORT_SYMBOL_GPL(vdpasim_schedule_work);
> > > > > 
> > > > >    static const struct vdpa_config_ops vdpasim_config_ops = {
> > > > >           .set_vq_address         = vdpasim_set_vq_address,
> > > > > @@ -704,6 +767,7 @@ 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 +801,7 @@ 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..da0866834918 100644
> > > > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> > > > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> > > > > @@ -53,7 +53,7 @@ struct vdpasim_dev_attr {
> > > > >    struct vdpasim {
> > > > >           struct vdpa_device vdpa;
> > > > >           struct vdpasim_virtqueue *vqs;
> > > > > -       struct work_struct work;
> > > > > +       struct delayed_work vring_work;
> > > > >           struct vdpasim_dev_attr dev_attr;
> > > > >           /* spinlock to synchronize virtqueue state */
> > > > >           spinlock_t lock;
> > > > > @@ -69,10 +69,13 @@ struct vdpasim {
> > > > >           bool running;
> > > > >           /* spinlock to synchronize iommu table */
> > > > >           spinlock_t iommu_lock;
> > > > > +       /* dummy notify page */
> > > > > +       unsigned long notify;
> > > > >    };
> > > > > 
> > > > >    struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr,
> > > > >                                  const struct vdpa_dev_set_config *config);
> > > > > +void vdpasim_schedule_work(struct vdpasim *vdpasim, bool sched_now);
> > > > > 
> > > > >    /* TODO: cross-endian support */
> > > > >    static inline bool vdpasim_is_little_endian(struct vdpasim *vdpasim)
> > > > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > > > > index c6db1a1baf76..8a640ea82284 100644
> > > > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > > > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
> > > > > @@ -288,7 +288,7 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
> > > > > 
> > > > >    static void vdpasim_blk_work(struct work_struct *work)
> > > > >    {
> > > > > -       struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
> > > > > +       struct vdpasim *vdpasim = container_of(work, struct vdpasim, vring_work.work);
> > > > >           bool reschedule = false;
> > > > >           int i;
> > > > > 
> > > > > @@ -325,8 +325,7 @@ static void vdpasim_blk_work(struct work_struct *work)
> > > > >    out:
> > > > >           spin_unlock(&vdpasim->lock);
> > > > > 
> > > > > -       if (reschedule)
> > > > > -               schedule_work(&vdpasim->work);
> > > > > +       vdpasim_schedule_work(vdpasim, reschedule);
> > > > >    }
> > > > > 
> > > > >    static void vdpasim_blk_get_config(struct vdpasim *vdpasim, void *config)
> > > > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > index c3cb225ea469..8b998952384b 100644
> > > > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > @@ -145,7 +145,7 @@ static void vdpasim_handle_cvq(struct vdpasim *vdpasim)
> > > > > 
> > > > >    static void vdpasim_net_work(struct work_struct *work)
> > > > >    {
> > > > > -       struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
> > > > > +       struct vdpasim *vdpasim = container_of(work, struct vdpasim, vring_work.work);
> > > > >           struct vdpasim_virtqueue *txq = &vdpasim->vqs[1];
> > > > >           struct vdpasim_virtqueue *rxq = &vdpasim->vqs[0];
> > > > >           ssize_t read, write;
> > > > > @@ -196,7 +196,7 @@ static void vdpasim_net_work(struct work_struct *work)
> > > > >                   vdpasim_net_complete(rxq, write);
> > > > > 
> > > > >                   if (++pkts > 4) {
> > > > > -                       schedule_work(&vdpasim->work);
> > > > > +                       vdpasim_schedule_work(vdpasim, true);
> > > > >                           goto out;
> > > > >                   }
> > > > >           }
> > > > > --
> > > > > 2.23.0
> > > > > 
> > > > 
> > > > .
> > 
> > .