On Wed, Jan 11, 2012 at 02:28:48PM +0000, Stefan Hajnoczi wrote: > On Wed, Jan 11, 2012 at 9:10 AM, Benjamin Herrenschmidt > <b...@kernel.crashing.org> wrote: > > On Wed, 2012-01-11 at 08:47 +0000, Stefan Hajnoczi wrote: > >> > >> This is also an opportunity to stop using CPU physical addresses in > >> the ring and instead perform DMA like a normal PCI device (use bus > >> addresses). > > > > Euh why ? > > Because it's a paravirt hack that ends up hitting corner cases. It's > not possible to do virtio-pci passthrough under nested virtualization > unless we use an IOMMU. Imagine passing virtio-net from L0 into the > L2 guest (i.e. PCI-passthrough). If virtio-pci is really "PCI" this > should be possible but it's not when we use physical addresses instead > of bus addresses. > > Stefan
It won't be hard to show siginificant performance regression if we do this. Hard to justify for something as niche as nested virt. -- MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
