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

[Kalra, Ashish]

Hello Jean,

Thanks for the information.

Is someone already working on implementing this, or is this something I can 
look into and implementing ?

Also, as Michael mentioned and I looked in the vfio iommu (type1) driver 
implementation that it supports mainly
static mappings of user-space processes with  user-space pages pinned/locked in 
memory, so a generic support
for ATS/PRI extensions needs to be added in VFIO too.

Thanks,
Ashish

-----Original Message-----
From: Jean-Philippe Brucker [mailto:address@hidden 
Sent: Friday, July 07, 2017 8:45 PM
To: Tian, Kevin; Kalra, Ashish; Auger Eric; Bharat Bhushan; address@hidden; 
address@hidden; address@hidden; address@hidden; address@hidden; address@hidden
Cc: address@hidden; address@hidden; address@hidden; address@hidden; 
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Subject: Re: [Qemu-arm] [Qemu-devel] [RFC v2 0/8] VIRTIO-IOMMU device

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