Re: [Qemu-arm] [Qemu-devel] [RFC v2 0/8] VIRTIO-IOMMU device

[Jean-Philippe Brucker]

Hi Ashish,

On 07/07/17 00:33, Tian, Kevin wrote:
>> From: Kalra, Ashish [mailto:address@hidden
>> Sent: Friday, July 7, 2017 7:24 AM
>>
>> I have a generic question on vIOMMU support, is there any proposal/plan to
>> add ATS/PRI extension support to vIOMMUs and allow
>> handling for end to end (v)IOMMU Page faults (w/t the device side
>> implementation on Vhost) ?
>>
>> Again, the motivation will be to do DMA on paged guest memory and
>> potentially avoiding the requirement of pinned/locked
>> guest physical memory for DMA.
> 
> yes, that's a necessary part to support SVM in both virtio-iommu 
> approach and fully emulated approach (e.g. for Intel VTd). There
> are already patches and discussions in other thread about how to
> propagate IOMMU page fault to vIOMMU. Then after it is done
> vIOMMU page fault emulation will be further added.
> 
> https://lkml.org/lkml/2017/6/27/964

For virtio-iommu, I'd like to add an event virtqueue for the device to
send page faults to the driver, in a format similar to a PRI Page Request.
The driver would then send a reply via the request virtqueue in a format
similar to a PRG Response.

In Qemu the device implementation would hopefully be based on the same
mechanism as VTd. The vhost implementation would receive IO Page Faults
from VFIO and forward them on the event virtqueue similarly to the
userspace implementation.

Thanks,
Jean