Re: [PATCH] vdpasim: support doorbell mapping

From: Michael S. Tsirkin
Date: Mon Nov 28 2022 - 09:18:59 EST

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On Mon, Nov 28, 2022 at 09:20:21PM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
>
>
> 在 2022/11/28 20:20, Michael S. Tsirkin 写道:
> > 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@xxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > From: Longpeng <longpeng2@xxxxxxxxxx>
> > > > > > >
> > > > > > > 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.
> >
>
> Um...The kick operation won't trigger VMEXIT if we support notify mapping
> for the vdpasim device.
> So, does the vdpasim device has to poll the notify
> address and then decide which VQ to poll?
> The pro of this approach is we can poll the notify address first instead of
> the unconditional poll the VQ, right?

Right. In fact you can do this without VIRTIO_F_NOTIFICATION_DATA too,
just write 0xffff before checking the vq.

>
> > > >
> > > > > > 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@xxxxxxxxxx>
> > > > > > > ---
> > > > > > > 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
> > > > > > >
> > > > > >
> > > > > > .
> > > >
> > > > .
> >
> > .

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