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

[Jason Wang <jasowang@redhat.com>]

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