On 10/11/2012 03:44 PM, Michael S. Tsirkin wrote: > On Thu, Oct 11, 2012 at 03:34:54PM +0200, Avi Kivity wrote: >> On 10/11/2012 03:31 PM, Michael S. Tsirkin wrote: >> > On Thu, Oct 11, 2012 at 03:27:03PM +0200, Avi Kivity wrote: >> >> vhost doesn't support guest iommus yet, indicate it to the user >> >> by gently depositing a core on their disk. >> >> >> >> Signed-off-by: Avi Kivity <a...@redhat.com> >> > >> > Actually there is no problem. virtio bypasses an IOMMU, >> > so vhost works fine by writing into guest memory directly. >> > >> > So I don't think we need this patch. >> >> The pci subsystem should set up the iommu so that it ignores virtio >> devices. If it does, an emulated iommu will not reach vhost. If it >> doesn't, then it will, and the assert() will alert us that we have a bug. > > You mean pci subsystem in the guest? I'm pretty sure that's not > the case at the moment: iommu is on by default and applies > to all devices unless you do something special. > I see where you are coming from but it does > not look right to break all existing guests.
No, qemu should configure virtio devices to bypass the iommu, even if it is on. > Also - I see no reason to single out vhost - I think same applies with > any virtio device, since it doesn't use the DMA API. True. -- error compiling committee.c: too many arguments to function
