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 <fb3a6ad0-dc79-9b58-3a32-06e3145a4dad@huawei.com>
In-Reply-To: <fb3a6ad0-dc79-9b58-3a32-06e3145a4dad@huawei.com>
From:   Jason Wang <jasowang@redhat.com>
Date:   Thu, 8 Dec 2022 15:37:26 +0800
Message-ID: <CACGkMEtgOArE-g8Frp0CkOZRa8F9YbHm5vSoN31X3-BxgT8YNA@mail.gmail.com>
Subject: Re: [PATCH v2] vdpasim: support doorbell mapping
To:     "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>
Cc:     stefanha@redhat.com, mst@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
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On Tue, Dec 6, 2022 at 4:46 PM Longpeng (Mike, Cloud Infrastructure
Service Product Dept.) <longpeng2@huawei.com> wrote:
>
>
>
> =E5=9C=A8 2022/12/6 14:59, Jason Wang =E5=86=99=E9=81=93:
> > On Mon, Dec 5, 2022 at 9:52 PM Longpeng(Mike) <longpeng2@huawei.com> wr=
ote:
> >>
> >> From: Longpeng <longpeng2@huawei.com>
> >>
> >> Support doorbell mapping for vdpasim devices, then we can test the not=
ify
> >> 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  p=
eriodic
> >> 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=3Dtrue
> >>
> >> 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 sp=
ace. 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: f=
alse)");
> >
> > 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 =
=3D {
> >>   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 =3D container_of(work, struct vdpasim, notify_work.wor=
k);
> >> +
> >> +       if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
> >> +               goto out;
> >> +
> >> +       if (!vdpasim->running)
> >> +               goto out;
> >> +
> >> +       val =3D (u16 *)vdpasim->notify;
> >> +       if (xchg(val, VDPASIM_NOTIFY_DEFVAL) !=3D VDPASIM_NOTIFY_DEFVA=
L)
> >> +               schedule_work(&vdpasim->work);
> >> +
> >> +out:
> >> +       schedule_delayed_work(&vdpasim->notify_work,
> >> +                             msecs_to_jiffies(VDPASIM_VRING_POLL_PERI=
OD));
> >> +}
> >> +
> >>   struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
> >>                                 const struct vdpa_dev_set_config *conf=
ig)
> >>   {
> >> @@ -287,6 +317,18 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev=
_attr *dev_attr,
> >>          set_dma_ops(dev, &vdpasim_dma_ops);
> >>          vdpasim->vdpa.mdev =3D dev_attr->mgmt_dev;
> >>
> >> +       if (notify_passthrough) {
> >> +               INIT_DELAYED_WORK(&vdpasim->notify_work, vdpasim_notif=
y_work);
> >> +
> >> +               vdpasim->notify =3D __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 =3D VDPASIM_NOTIFY_DEFVAL;
> >
> > WRITE_ONCE()?
> >
> Okay.
>
> >> +       }
> >> +
> >>          vdpasim->config =3D 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 sta=
rt)
> >> +{
> >> +       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_P=
OLL_PERIOD));
> >> +       else
> >> +               cancel_delayed_work_sync(&vdpasim->notify_work);
> >> +}
> >> +
> >>   static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
> >>   {
> >>          struct vdpasim *vdpasim =3D vdpa_to_sim(vdpa);
> >> @@ -502,12 +556,14 @@ static void vdpasim_set_status(struct vdpa_devic=
e *vdpa, u8 status)
> >>          spin_lock(&vdpasim->lock);
> >>          vdpasim->status =3D status;
> >>          spin_unlock(&vdpasim->lock);
> >> +       vdpasim_set_notify_work(vdpasim, status & VIRTIO_CONFIG_S_DRIV=
ER_OK);
> >>   }
> >>
> >>   static int vdpasim_reset(struct vdpa_device *vdpa, bool clear)
> >>   {
> >>          struct vdpasim *vdpasim =3D vdpa_to_sim(vdpa);
> >>
> >> +       vdpasim_set_notify_work(vdpasim, false);
> >>          spin_lock(&vdpasim->lock);
> >>          vdpasim->status =3D 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 =3D vdpa_to_sim(vdpa);
> >> +       struct vdpa_notification_area notify;
> >> +
> >> +       notify.addr =3D virt_to_phys((void *)vdpasim->notify);
> >> +       notify.size =3D PAGE_SIZE;
> >> +
> >> +       return notify;
> >> +}
> >> +
> >>   static void vdpasim_free(struct vdpa_device *vdpa)
> >>   {
> >>          struct vdpasim *vdpasim =3D vdpa_to_sim(vdpa);
> >>          int i;
> >>
> >> +       vdpasim_set_notify_work(vdpasim, false);
> >>          cancel_work_sync(&vdpasim->work);
> >>
> >>          for (i =3D 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 =3D {
> >> @@ -704,6 +779,7 @@ static const struct vdpa_config_ops vdpasim_config=
_ops =3D {
> >>          .get_vq_ready           =3D vdpasim_get_vq_ready,
> >>          .set_vq_state           =3D vdpasim_set_vq_state,
> >>          .get_vq_state           =3D vdpasim_get_vq_state,
> >> +       .get_vq_notification    =3D vdpasim_get_vq_notification,
> >>          .get_vq_align           =3D vdpasim_get_vq_align,
> >>          .get_vq_group           =3D vdpasim_get_vq_group,
> >>          .get_device_features    =3D vdpasim_get_device_features,
> >> @@ -737,6 +813,7 @@ static const struct vdpa_config_ops vdpasim_batch_=
config_ops =3D {
> >>          .get_vq_ready           =3D vdpasim_get_vq_ready,
> >>          .set_vq_state           =3D vdpasim_set_vq_state,
> >>          .get_vq_state           =3D vdpasim_get_vq_state,
> >> +       .get_vq_notification    =3D vdpasim_get_vq_notification,
> >>          .get_vq_align           =3D vdpasim_get_vq_align,
> >>          .get_vq_group           =3D vdpasim_get_vq_group,
> >>          .get_device_features    =3D 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
> >>
> >
> > .
>