On Tue, Jul 28, 2015 at 02:46:20PM +0200, Paolo Bonzini wrote: > > > On 28/07/2015 12:12, Benjamin Herrenschmidt wrote: > >> > That is an experimental feature (it's x-iommu), so it can change. > >> > > >> > The plan was: > >> > > >> > - for PPC, virtio never honors IOMMU > >> > > >> > - for non-PPC, either have virtio always honor IOMMU, or enforce that > >> > virtio is not under IOMMU. > >> > > > I dislike having PPC special cased. > > > > In fact, today x86 guests also assume that virtio bypasses IOMMU I > > believe. In fact *all* guests do. > > This doesn't matter much, since the only guests that implement an IOMMU > in QEMU are (afaik) PPC and x86, and x86 does not yet promise any kind > of stability.
Hmm I think Jan (cc) said it was already used out there. > > I would much prefer if the information as to whether it honors or not > > gets passed to the guest somewhat. My preference goes for passing it via > > the virtio config space but there were objections that it should be a > > bus property (which is tricky to do with PCI and doesn't properly > > reflect the fact that in qemu you can mix & match IOMMU-honoring devices > > and bypassing-virtio on the same bus). > > Yes, for example on x86 it must be passed through the DMAR table. > virtio-pci device must have a separate DRHD for them. In QEMU, you > could add an "under-iommu" property to PCI bridges, and walk the > hierarchy of bridges to build the DRHDs. > > Paolo -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
