On 10/15/2012 10:44 AM, liu ping fan wrote: > On Thu, Oct 11, 2012 at 11:48 PM, Avi Kivity <a...@redhat.com> 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?
The exception is not just for vhost, but for every virtio device. So the iommu needs to be aware of that, and if it manages a virtio device, it needs to provide a 1:1 translation. -- error compiling committee.c: too many arguments to function