On Thu, 5 Mar 2020 15:30:07 +1100
David Gibson <da...@gibson.dropbear.id.au> wrote:
> Upcoming Secure VM support for pSeries machines introduces some
> complications for virtio, since the transfer buffers need to be
> explicitly shared so that the hypervisor can access them.
>
> While it's not strictly speaking dependent on it, the fact that virtio
> devices bypass normal platform IOMMU translation complicates the issue
> on the guest side. Since there are some significan downsides to
> bypassing the vIOMMU anyway, let's just disable that.
>
> There's already a flag to do this in virtio, just turn it on by
> default for forthcoming pseries machine types.
>
> Any opinions on whether dropping support for the older guest kernels
> is acceptable at this point?
>
> Changes since v2:
> * Rebase and improve some comments
> Changes since v1:
> * Added information on which guest kernel versions will no longer
> work with these changes
> * Use Michael Tsirkin's suggested better way of handling the machine
> type change
>
> David Gibson (2):
> spapr: Disable legacy virtio devices for pseries-5.0 and later
This disables legacy AND transitional devices. IIUC this first patch
is needed because only non-transitional (pure virtio-1) devices
support iommu_platform=on, ie. this check in virtio_pci_device_plugged():
if (legacy) {
if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
error_setg(errp, "VIRTIO_F_IOMMU_PLATFORM was supported by"
" neither legacy nor transitional device");
return ;
}
It certainly looks right for legacy devices but what about
transitional ones ? I couldn't find any indication in the
spec or in the QEMU archives that explains why IOMMU should
only be used with non-transitional devices...
Jason or Michael, can you explain ?
> spapr: Enable virtio iommu_platform=on by default
>
> hw/ppc/spapr.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
