Re: [PATCH v1] vhost-vdpa: Set discarding of RAM broken when initializing the backend

[Jason Wang]

On 2021/3/4 5:34 下午, David Hildenbrand wrote:
> On 04.03.21 10:32, Jason Wang wrote:
> > On 2021/3/3 6:26 下午, David Hildenbrand wrote:
> > > On 03.03.21 03:53, Jason Wang wrote:
> > > > On 2021/3/3 12:21 上午, David Hildenbrand wrote:
> > > > > Similar to VFIO, vDPA will go ahead an map+pin all guest memory. 
> > > > > Memory
> > > > > that used to be discarded will get re-populated and if we
> > > > > discard+re-access memory after mapping+pinning, the pages mapped
> > > > > into the
> > > > > vDPA IOMMU will go out of sync with the actual pages mapped into the
> > > > > user
> > > > > space page tables.
> > > > >
> > > > > Set discarding of RAM broken such that:
> > > > > - virtio-mem and vhost-vdpa run mutually exclusive
> > > > > - virtio-balloon is inhibited and no memory discards will get issued
> > > > >
> > > > > In the future, we might be able to support coordinated discarding of
> > > > > RAM
> > > > > as used by virtio-mem and as planned for VFIO.
> > > > >
> > > > > Cc: Jason Wang <jasowang@redhat.com>
> > > > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > > > Cc: Cindy Lu <lulu@redhat.com>
> > > > > Signed-off-by: David Hildenbrand <david@redhat.com>
> > > >
> > > >
> > > > Acked-by: Jason Wang <jasowang@redhat.com>
> > > >
> > > >
> > > > > ---
> > > > >
> > > > > Note: I was not actually able to reproduce/test as I fail to get the
> > > > > vdpa_sim/vdpa_sim_net running on upstream Linux (whetever vdpa,
> > > > > vhost_vdpa,
> > > > > vdpa_sim, vdpa_sim_net modules I probe, and in which order, no vdpa
> > > > > devices
> > > > > appear under /sys/bus/vdpa/devices/ or /dev/).
> > > >
> > > >
> > > > The device creation was switched to use vdpa tool that is integrated
> > > > with iproue2[1].
> > > >
> > > > [1]
> > > > https://git.kernel.org/pub/scm/network/iproute2/iproute2-next.git/commit/?id=143610383da51e1f868c6d5a2a5e2fb552293d18 
> > >
> > > It would be great to document that somewhere if not already done. I
> > > only found older RH documentations that were not aware of that. I'll
> > > give it a try - thanks!
> >
> >
> > Will think about this. Which RH doc do you refer here? Is this the
> > redhat blog?
>
> https://www.redhat.com/en/blog/hands-vdpa-what-do-you-do-when-you-aint-got-hardware 
>
>
> As it's supposed to be from October 14, 2020 I was surprised to not 
> get it running (even with older kernels IIRC).


Right, the mgmt API is just merged. Will try to see if we can fix the blog.

Thanks