Re: [Qemu-devel] [RFC v1 7/7] vhost: abort if an emulated iommu is used

[liu ping fan]

On Thu, Oct 11, 2012 at 11:48 PM, Avi Kivity <address@hidden> wrote:
> On 10/11/2012 05:34 PM, Michael S. Tsirkin wrote:
>> On Thu, Oct 11, 2012 at 04:35:23PM +0200, Avi Kivity wrote:
>>> On 10/11/2012 04:35 PM, Michael S. Tsirkin wrote:
>>>
>>> >> No, qemu should configure virtio devices to bypass the iommu, even if it
>>> >> is on.
>>> >
>>> > Okay so there will be some API that virtio devices should call
>>> > to achieve this?
>>>
>>> The iommu should probably call pci_device_bypasses_iommu() to check for
>>> such devices.
>>
>> So maybe this patch should depend on the introduction of such
>> an API.
>
> I've dropped it for now.
>
> In fact, virtio/vhost are safe since they use cpu_physical_memory_rw()
> and the memory listener watches address_space_memory, no iommu there.

Not quite sure your meaning.  My understanding is that as a pci
device, vhost can lie behind a iommu in topology, which result in the
transaction launched can be snapped by the emulated iommu. BUT we make
a exception for vhost-dev and enforce
address_space_rw(address_space_memory, ..) NOT
address_space_rw(pci_dev->bus_master_as,..)  for vhost device, so we
bypass the iommu.  Right?

Regards,
pingfan
> vfio needs to change to listen to pci_dev->bus_master_as, and need
> special handling for iommu regions (abort for now, type 2 iommu later).
>
> --
> error compiling committee.c: too many arguments to function