Re: [PATCH] vhost: introduce vDPA based backend

[Jason Wang]

On 2020/2/5 äå3:15, Shahaf Shuler wrote:
> Wednesday, February 5, 2020 4:03 AM, Tiwei Bie:
> > Subject: Re: [PATCH] vhost: introduce vDPA based backend
> >
> > On Tue, Feb 04, 2020 at 11:30:11AM +0800, Jason Wang wrote:
> > > On 2020/1/31 äå11:36, Tiwei Bie wrote:
> > > > This patch introduces a vDPA based vhost backend. This backend is
> > > > built on top of the same interface defined in virtio-vDPA and
> > > > provides a generic vhost interface for userspace to accelerate the
> > > > virtio devices in guest.
> > > >
> > > > This backend is implemented as a vDPA device driver on top of the
> > > > same ops used in virtio-vDPA. It will create char device entry named
> > > > vhost-vdpa/$vdpa_device_index for userspace to use. Userspace can
> > > > use vhost ioctls on top of this char device to setup the backend.
> > > >
> > > > Signed-off-by: Tiwei Bie <tiwei.bie@xxxxxxxxx>
> [...]
>
> > > > +static long vhost_vdpa_do_dma_mapping(struct vhost_vdpa *v) {
> > > > +	/* TODO: fix this */
> > >
> > > Before trying to do this it looks to me we need the following during
> > > the probe
> > >
> > > 1) if set_map() is not supported by the vDPA device probe the IOMMU
> > > that is supported by the vDPA device
> > > 2) allocate IOMMU domain
> > >
> > > And then:
> > >
> > > 3) pin pages through GUP and do proper accounting
> > > 4) store GPA->HPA mapping in the umem
> > > 5) generate diffs of memory table and using IOMMU API to setup the dma
> > > mapping in this method
> > >
> > > For 1), I'm not sure parent is sufficient for to doing this or need to
> > > introduce new API like iommu_device in mdev.
> > Agree. We may also need to introduce something like the iommu_device.
> Would it be better for the map/umnap logic to happen inside each device ?
> Devices that needs the IOMMU will call iommu APIs from inside the driver callback.


Technically, this can work. But if it can be done by vhost-vpda it will 
make the vDPA driver more compact and easier to be implemented.


> Devices that has other ways to do the DMA mapping will call the proprietary APIs.


To confirm, do you prefer:

1) map/unmap

or

2) pass all maps at one time?

Thanks


>