On Thu, Aug 02, 2018 at 10:33:05AM -0500, Benjamin Herrenschmidt wrote: > On Thu, 2018-08-02 at 00:56 +0300, Michael S. Tsirkin wrote: > > > but it's not, VMs are > > > created in "legacy" mode all the times and we don't know at VM creation > > > time whether it will become a secure VM or not. The way our secure VMs > > > work is that they start as a normal VM, load a secure "payload" and > > > call the Ultravisor to "become" secure. > > > > > > So we're in a bit of a bind here. We need that one-liner optional arch > > > hook to make virtio use swiotlb in that "IOMMU bypass" case. > > > > > > Ben. > > > > And just to make sure I understand, on your platform DMA APIs do include > > some of the cache flushing tricks and this is why you don't want to > > declare iommu support in the hypervisor? > > I'm not sure I parse what you mean. > > We don't need cache flushing tricks. You don't but do real devices on same platform need them? > The problem we have with our > "secure" VMs is that: > > - At VM creation time we have no idea it's going to become a secure > VM, qemu doesn't know anything about it, and thus qemu (or other > management tools, libvirt etc...) are going to create "legacy" (ie > iommu bypass) virtio devices. > > - Once the VM goes secure (early during boot but too late for qemu), > it will need to make virtio do bounce-buffering via swiotlb because > qemu cannot physically access most VM pages (blocked by HW security > features), we need to bounce buffer using some unsecure pages that are > accessible to qemu. > > That said, I wouldn't object for us to more generally switch long run > to changing qemu so that virtio on powerpc starts using the IOMMU as a > default provided we fix our guest firmware to understand it (it > currently doesn't), and provided we verify that the performance impact > on things like vhost is negligible. > > Cheers, > Ben. > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
