On Tue, Apr 19, 2016 at 11:01:38AM -0700, Andy Lutomirski wrote: > On Tue, Apr 19, 2016 at 10:49 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Tue, Apr 19, 2016 at 12:26:44PM -0400, David Woodhouse wrote: > >> On Tue, 2016-04-19 at 19:20 +0300, Michael S. Tsirkin wrote: > >> > > >> > > I thought that PLATFORM served that purpose. Woudn't the host > >> > > advertise PLATFORM support and, if the guest doesn't ack it, the host > >> > > device would skip translation? Or is that problematic for vfio? > >> > > >> > Exactly that's problematic for security. > >> > You can't allow guest driver to decide whether device skips security. > >> > >> Right. Because fundamentally, this *isn't* a property of the endpoint > >> device, and doesn't live in virtio itself. > >> > >> It's a property of the platform IOMMU, and lives there. > > > > It's a property of the hypervisor virtio implementation, and lives there. > > It is now, but QEMU could, in principle, change the way it thinks > about it so that virtio devices would use the QEMU DMA API but ask > QEMU to pass everything through 1:1. This would be entirely invisible > to guests but would make it be a property of the IOMMU implementation. > At that point, maybe QEMU could find a (platform dependent) way to > tell the guest what's going on. > > FWIW, as far as I can tell, PPC and SPARC really could, in principle, > set up 1:1 mappings in the guest so that the virtio devices would work > regardless of whether QEMU is ignoring the IOMMU or not -- I think the > only obstacle is that the PPC and SPARC 1:1 mappings are currectly set > up with an offset. I don't know too much about those platforms, but > presumably the layout could be changed so that 1:1 really was 1:1. > > --Andy Sure. Do you see any reason why the decision to do this can't be keyed off the virtio feature bit? -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
