Re: [PATCH v2] vdpasim: support doorbell mapping
From: Jason Wang
Date: Thu Dec 08 2022 - 02:38:43 EST
On Tue, Dec 6, 2022 at 4:46 PM Longpeng (Mike, Cloud Infrastructure
Service Product Dept.) <longpeng2@xxxxxxxxxx> wrote:
>
>
>
> 在 2022/12/6 14:59, Jason Wang 写道:
> > On Mon, Dec 5, 2022 at 9:52 PM 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.
> >>
> >> 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@xxxxxxxxxx>
> >> ---
> >> 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).
> >
> We can support kick mode and passthgourh mode simultaneously now, it is
> a little unnecessary. I would remove it in next version.
>
> >> +
> >> #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?
> >
> Oh, I had replied you in that thread.
>
> The vm_page_prot of notify mapping VMA 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.
Ok, but any reason to have a X86 guard for this? This basically makes
it won't work for non-x86 archs?
I think the correct way is to introduce a new config_ops to fetch the
correct pgprot. Then we are fine.
Thanks
>
> Otherwise, 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
>
> >> + *(u16 *)vdpasim->notify = VDPASIM_NOTIFY_DEFVAL;
> >
> > WRITE_ONCE()?
> >
> Okay.
>
> >> + }
> >> +
> >> 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().
> >
> Okay, thanks.
>
> > 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
> >>
> >
> > .
>