by Jason Wang

[permalink] [raw]

Subject: Re: [PATCH] vdpasim: support doorbell mapping

On Mon, Nov 28, 2022 at 10:36 PM Longpeng (Mike, Cloud Infrastructure
Service Product Dept.) <[email protected]> wrote:
>
>
>
> 在 2022/11/28 22:17, Michael S. Tsirkin 写道:
> > 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) <[email protected]> wrote:
> >>>>>>>>
> >>>>>>>> From: Longpeng <[email protected]>
> >>>>>>>>
> >>>>>>>> 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.
> >
> Yes, this can work. I will try it in the next version if there're no
> other objections.

Yes, please.

Thanks

>
> >>
> >>>>>
> >>>>>>> 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 <[email protected]>
> >>>>>>>> ---
> >>>>>>>> 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
> >>>>>>>>
> >>>>>>>
> >>>>>>> .
> >>>>>
> >>>>> .
> >>>
> >>> .
> >
> > .
>